Why do people move from one county or region to another? The usual suspects are jobs, family, significant others, and overall cost of living, but there are other elements at play. For those with children, moving within close proximity of a highly rated school district is a key contributing factor. For younger adults just starting out, living someplace with a vibrant social scene might be a top priority. And for those whose careers have wound down after a lifetime of work, finding retirement-friendly communities is the goal—communities deemed to be safe, offer accessibility to medical resources and leisure activities in equal measure, and be affordable for those on a limited income.

This is, of course, by no means an exhaustive list. People’s reasons for choosing to live where they do are as diverse as people themselves.

As far as why certain counties across the U.S. have experienced growth, relocation is not the sole, or even primary, reason why. While more than 1,800 counties saw population gains in 2021, approximately 73% of all U.S. counties saw what the U.S. Census Bureau characterizes as a natural decrease. This was a significant jump from 2020, when 55.5% of countries experienced such a decrease. According to the Bureau, natural decrease is the simple result of “when there are more deaths than births in a population over a given time period.” In 2021, the conflation of fewer births with an aging population that was also absorbing a higher-than-usual mortality rate due to the ongoing COVID-19 pandemic led to this “increased decrease.”

Nonetheless, as stated 1,800 counties nationwide have grown larger over the last year, and a sizable percentage of them are in Illinois. Stacker compiled a list of the fastest-growing counties in Illinois using data from the U.S. Census Bureau. Counties are ranked by the highest population growth from 2010 to 2020, based on the U.S. Decennial Census.

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#50. Marshall County

– 2010 to 2020 population change: -898
— #2,438 among all counties nationwide
– 2010 to 2020 percent population change: -7.1%
— #74 among counties in Illinois, #2,633 among all counties nationwide
– 2020 population: 11,742
— #85 largest county in Illinois, #2,297 largest county nationwide

#49. Clark County

– 2010 to 2020 population change: -880
— #2,425 among all counties nationwide
– 2010 to 2020 percent population change: -5.4%
— #57 among counties in Illinois, #2,384 among all counties nationwide
– 2020 population: 15,455
— #71 largest county in Illinois, #2,064 largest county nationwide

#48. Warren County

– 2010 to 2020 population change: -872
— #2,421 among all counties nationwide
– 2010 to 2020 percent population change: -4.9%
— #52 among counties in Illinois, #2,317 among all counties nationwide
– 2020 population: 16,835
— #63 largest county in Illinois, #1,979 largest county nationwide

#47. Clinton County

– 2010 to 2020 population change: -863
— #2,415 among all counties nationwide
– 2010 to 2020 percent population change: -2.3%
— #26 among counties in Illinois, #1,890 among all counties nationwide
– 2020 population: 36,899
— #38 largest county in Illinois, #1,256 largest county nationwide

#46. White County

– 2010 to 2020 population change: -788
— #2,379 among all counties nationwide
– 2010 to 2020 percent population change: -5.4%
— #56 among counties in Illinois, #2,380 among all counties nationwide
– 2020 population: 13,877
— #76 largest county in Illinois, #2,164 largest county nationwide

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#45. Christian County

– 2010 to 2020 population change: -768
— #2,369 among all counties nationwide
– 2010 to 2020 percent population change: -2.2%
— #25 among counties in Illinois, #1,881 among all counties nationwide
– 2020 population: 34,032
— #43 largest county in Illinois, #1,328 largest county nationwide

#44. Mercer County

– 2010 to 2020 population change: -735
— #2,351 among all counties nationwide
– 2010 to 2020 percent population change: -4.5%
— #46 among counties in Illinois, #2,235 among all counties nationwide
– 2020 population: 15,699
— #69 largest county in Illinois, #2,048 largest county nationwide

#43. Boone County

– 2010 to 2020 population change: -717
— #2,344 among all counties nationwide
– 2010 to 2020 percent population change: -1.3%
— #21 among counties in Illinois, #1,710 among all counties nationwide
– 2020 population: 53,448
— #25 largest county in Illinois, #943 largest county nationwide

#42. Pope County

– 2010 to 2020 population change: -707
— #2,335 among all counties nationwide
– 2010 to 2020 percent population change: -15.8%
— #100 among counties in Illinois, #3,062 among all counties nationwide
– 2020 population: 3,763
— #101 largest county in Illinois, #2,902 largest county nationwide

#41. Brown County

– 2010 to 2020 population change: -693
— #2,325 among all counties nationwide
– 2010 to 2020 percent population change: -10.0%
— #89 among counties in Illinois, #2,864 among all counties nationwide
– 2020 population: 6,244
— #93 largest county in Illinois, #2,718 largest county nationwide

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#40. Hardin County

– 2010 to 2020 population change: -671
— #2,303 among all counties nationwide
– 2010 to 2020 percent population change: -15.5%
— #98 among counties in Illinois, #3,057 among all counties nationwide
– 2020 population: 3,649
— #102 largest county in Illinois, #2,913 largest county nationwide

#39. Calhoun County

– 2010 to 2020 population change: -652
— #2,287 among all counties nationwide
– 2010 to 2020 percent population change: -12.8%
— #94 among counties in Illinois, #2,987 among all counties nationwide
– 2020 population: 4,437
— #100 largest county in Illinois, #2,860 largest county nationwide

#38. Fayette County

– 2010 to 2020 population change: -652
— #2,287 among all counties nationwide
– 2010 to 2020 percent population change: -2.9%
— #31 among counties in Illinois, #1,988 among all counties nationwide
– 2020 population: 21,488
— #55 largest county in Illinois, #1,741 largest county nationwide

#37. Gallatin County

– 2010 to 2020 population change: -643
— #2,278 among all counties nationwide
– 2010 to 2020 percent population change: -11.5%
— #92 among counties in Illinois, #2,947 among all counties nationwide
– 2020 population: 4,946
— #99 largest county in Illinois, #2,828 largest county nationwide

#36. Jo Daviess County

– 2010 to 2020 population change: -643
— #2,278 among all counties nationwide
– 2010 to 2020 percent population change: -2.8%
— #30 among counties in Illinois, #1,974 among all counties nationwide
– 2020 population: 22,035
— #53 largest county in Illinois, #1,713 largest county nationwide

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#35. Schuyler County

– 2010 to 2020 population change: -642
— #2,275 among all counties nationwide
– 2010 to 2020 percent population change: -8.5%
— #81 among counties in Illinois, #2,751 among all counties nationwide
– 2020 population: 6,902
— #90 largest county in Illinois, #2,667 largest county nationwide

#34. Cass County

– 2010 to 2020 population change: -600
— #2,244 among all counties nationwide
– 2010 to 2020 percent population change: -4.4%
— #43 among counties in Illinois, #2,226 among all counties nationwide
– 2020 population: 13,042
— #82 largest county in Illinois, #2,212 largest county nationwide

#33. Cumberland County

– 2010 to 2020 population change: -598
— #2,241 among all counties nationwide
– 2010 to 2020 percent population change: -5.4%
— #58 among counties in Illinois, #2,390 among all counties nationwide
– 2020 population: 10,450
— #87 largest county in Illinois, #2,382 largest county nationwide

#32. Stark County

– 2010 to 2020 population change: -594
— #2,239 among all counties nationwide
– 2010 to 2020 percent population change: -9.9%
— #88 among counties in Illinois, #2,854 among all counties nationwide
– 2020 population: 5,400
— #95 largest county in Illinois, #2,786 largest county nationwide

#31. Wabash County

– 2010 to 2020 population change: -586
— #2,232 among all counties nationwide
– 2010 to 2020 percent population change: -4.9%
— #51 among counties in Illinois, #2,312 among all counties nationwide
– 2020 population: 11,361
— #86 largest county in Illinois, #2,324 largest county nationwide

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#30. Wayne County

– 2010 to 2020 population change: -581
— #2,231 among all counties nationwide
– 2010 to 2020 percent population change: -3.5%
— #37 among counties in Illinois, #2,071 among all counties nationwide
– 2020 population: 16,179
— #66 largest county in Illinois, #2,022 largest county nationwide

#29. Union County

– 2010 to 2020 population change: -564
— #2,209 among all counties nationwide
– 2010 to 2020 percent population change: -3.2%
— #33 among counties in Illinois, #2,026 among all counties nationwide
– 2020 population: 17,244
— #61 largest county in Illinois, #1,952 largest county nationwide

#28. Ford County

– 2010 to 2020 population change: -547
— #2,196 among all counties nationwide
– 2010 to 2020 percent population change: -3.9%
— #40 among counties in Illinois, #2,146 among all counties nationwide
– 2020 population: 13,534
— #78 largest county in Illinois, #2,183 largest county nationwide

#27. Clay County

– 2010 to 2020 population change: -527
— #2,169 among all counties nationwide
– 2010 to 2020 percent population change: -3.8%
— #39 among counties in Illinois, #2,134 among all counties nationwide
– 2020 population: 13,288
— #80 largest county in Illinois, #2,197 largest county nationwide

#26. Edwards County

– 2010 to 2020 population change: -476
— #2,120 among all counties nationwide
– 2010 to 2020 percent population change: -7.1%
— #73 among counties in Illinois, #2,628 among all counties nationwide
– 2020 population: 6,245
— #92 largest county in Illinois, #2,717 largest county nationwide

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#25. Hamilton County

– 2010 to 2020 population change: -464
— #2,106 among all counties nationwide
– 2010 to 2020 percent population change: -5.5%
— #59 among counties in Illinois, #2,404 among all counties nationwide
– 2020 population: 7,993
— #89 largest county in Illinois, #2,579 largest county nationwide

#24. Richland County

– 2010 to 2020 population change: -420
— #2,068 among all counties nationwide
– 2010 to 2020 percent population change: -2.6%
— #29 among counties in Illinois, #1,941 among all counties nationwide
– 2020 population: 15,813
— #67 largest county in Illinois, #2,041 largest county nationwide

#23. Jasper County

– 2010 to 2020 population change: -411
— #2,054 among all counties nationwide
– 2010 to 2020 percent population change: -4.2%
— #41 among counties in Illinois, #2,199 among all counties nationwide
– 2020 population: 9,287
— #88 largest county in Illinois, #2,468 largest county nationwide

#22. Menard County

– 2010 to 2020 population change: -408
— #2,049 among all counties nationwide
– 2010 to 2020 percent population change: -3.2%
— #35 among counties in Illinois, #2,037 among all counties nationwide
– 2020 population: 12,297
— #83 largest county in Illinois, #2,256 largest county nationwide

#21. Scott County

– 2010 to 2020 population change: -406
— #2,048 among all counties nationwide
– 2010 to 2020 percent population change: -7.6%
— #76 among counties in Illinois, #2,677 among all counties nationwide
– 2020 population: 4,949
— #98 largest county in Illinois, #2,827 largest county nationwide

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#20. Putnam County

– 2010 to 2020 population change: -369
— #2,002 among all counties nationwide
– 2010 to 2020 percent population change: -6.1%
— #67 among counties in Illinois, #2,492 among all counties nationwide
– 2020 population: 5,637
— #94 largest county in Illinois, #2,768 largest county nationwide

#19. Moultrie County

– 2010 to 2020 population change: -320
— #1,940 among all counties nationwide
– 2010 to 2020 percent population change: -2.2%
— #24 among counties in Illinois, #1,877 among all counties nationwide
– 2020 population: 14,526
— #74 largest county in Illinois, #2,116 largest county nationwide

#18. Douglas County

– 2010 to 2020 population change: -240
— #1,829 among all counties nationwide
– 2010 to 2020 percent population change: -1.2%
— #19 among counties in Illinois, #1,690 among all counties nationwide
– 2020 population: 19,740
— #58 largest county in Illinois, #1,831 largest county nationwide

#17. Woodford County

– 2010 to 2020 population change: -197
— #1,769 among all counties nationwide
– 2010 to 2020 percent population change: -0.5%
— #17 among counties in Illinois, #1,574 among all counties nationwide
– 2020 population: 38,467
— #34 largest county in Illinois, #1,213 largest county nationwide

#16. Piatt County

– 2010 to 2020 population change: -56
— #1,571 among all counties nationwide
– 2010 to 2020 percent population change: -0.3%
— #16 among counties in Illinois, #1,552 among all counties nationwide
– 2020 population: 16,673
— #65 largest county in Illinois, #1,992 largest county nationwide

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#15. Carroll County

– 2010 to 2020 population change: +315
— #1,247 among all counties nationwide
– 2010 to 2020 percent population change: +2.0%
— #7 among counties in Illinois, #1,176 among all counties nationwide
– 2020 population: 15,702
— #68 largest county in Illinois, #2,047 largest county nationwide

#14. Effingham County

– 2010 to 2020 population change: +426
— #1,191 among all counties nationwide
– 2010 to 2020 percent population change: +1.2%
— #11 among counties in Illinois, #1,298 among all counties nationwide
– 2020 population: 34,668
— #41 largest county in Illinois, #1,308 largest county nationwide

#13. Johnson County

– 2010 to 2020 population change: +726
— #1,080 among all counties nationwide
– 2010 to 2020 percent population change: +5.8%
— #3 among counties in Illinois, #744 among all counties nationwide
– 2020 population: 13,308
— #79 largest county in Illinois, #2,195 largest county nationwide

#12. Williamson County

– 2010 to 2020 population change: +796
— #1,059 among all counties nationwide
– 2010 to 2020 percent population change: +1.2%
— #12 among counties in Illinois, #1,310 among all counties nationwide
– 2020 population: 67,153
— #22 largest county in Illinois, #798 largest county nationwide

#11. Kane County

– 2010 to 2020 population change: +1,253
— #952 among all counties nationwide
– 2010 to 2020 percent population change: +0.2%
— #15 among counties in Illinois, #1,451 among all counties nationwide
– 2020 population: 516,522
— #5 largest county in Illinois, #140 largest county nationwide

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#10. McLean County

– 2010 to 2020 population change: +1,382
— #931 among all counties nationwide
– 2010 to 2020 percent population change: +0.8%
— #13 among counties in Illinois, #1,363 among all counties nationwide
– 2020 population: 170,954
— #13 largest county in Illinois, #388 largest county nationwide

#9. McHenry County

– 2010 to 2020 population change: +1,469
— #912 among all counties nationwide
– 2010 to 2020 percent population change: +0.5%
— #14 among counties in Illinois, #1,417 among all counties nationwide
– 2020 population: 310,229
— #6 largest county in Illinois, #230 largest county nationwide

#8. Monroe County

– 2010 to 2020 population change: +2,005
— #815 among all counties nationwide
– 2010 to 2020 percent population change: +6.1%
— #2 among counties in Illinois, #706 among all counties nationwide
– 2020 population: 34,962
— #40 largest county in Illinois, #1,300 largest county nationwide

#7. Grundy County

– 2010 to 2020 population change: +2,470
— #753 among all counties nationwide
– 2010 to 2020 percent population change: +4.9%
— #4 among counties in Illinois, #830 among all counties nationwide
– 2020 population: 52,533
— #27 largest county in Illinois, #958 largest county nationwide

#6. Champaign County

– 2010 to 2020 population change: +4,784
— #578 among all counties nationwide
– 2010 to 2020 percent population change: +2.4%
— #6 among counties in Illinois, #1,132 among all counties nationwide
– 2020 population: 205,865
— #10 largest county in Illinois, #333 largest county nationwide

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#5. Lake County

– 2010 to 2020 population change: +10,880
— #407 among all counties nationwide
– 2010 to 2020 percent population change: +1.5%
— #10 among counties in Illinois, #1,247 among all counties nationwide
– 2020 population: 714,342
— #3 largest county in Illinois, #97 largest county nationwide

#4. DuPage County

– 2010 to 2020 population change: +15,953
— #336 among all counties nationwide
– 2010 to 2020 percent population change: +1.7%
— #8 among counties in Illinois, #1,221 among all counties nationwide
– 2020 population: 932,877
— #2 largest county in Illinois, #59 largest county nationwide

#3. Kendall County

– 2010 to 2020 population change: +17,133
— #320 among all counties nationwide
– 2010 to 2020 percent population change: +14.9%
— #1 among counties in Illinois, #229 among all counties nationwide
– 2020 population: 131,869
— #15 largest county in Illinois, #489 largest county nationwide

#2. Will County

– 2010 to 2020 population change: +18,795
— #305 among all counties nationwide
– 2010 to 2020 percent population change: +2.8%
— #5 among counties in Illinois, #1,087 among all counties nationwide
– 2020 population: 696,355
— #4 largest county in Illinois, #98 largest county nationwide

#1. Cook County

– 2010 to 2020 population change: +80,866
— #64 among all counties nationwide
– 2010 to 2020 percent population change: +1.6%
— #9 among counties in Illinois, #1,244 among all counties nationwide
– 2020 population: 5,275,541
— #1 largest county in Illinois, #2 largest county nationwide

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