The shooting occurred shortly after 1 p.m. near the intersection of W. Main Street and Glenview Drive, police said.
The victims were identified as a 57-year-old woman and her 27-year-old son. The shooting started outside the female victim's home, but police were investigating inside the residence as well.
The woman was shot twice and her son shot once. Both victims were conscious and taken to a hospital.
A neighbor said the 27-year-old was on his way to becoming a church minister and was a mentor to many children in the neighborhood.
Police described the suspect as an African-American man in his late 20s or early 30s, with a slim build, and wearing dark clothes. He was last seen driving an older model, white Chevy Impala.
Anyone with information on this case is asked to contact the Belleville Police Department at 618-234-1218 (x1686).