"Jason Plummer is the strongest candidate we've had in years," said Jon McLean, chairman of the St. Clair Co. Republican Committee.
Democratic incumbent Costello announced in October he would retire at the end of his term in January 2013. He followed Congressman Mel Price who held the seat for nearly fifty years.
Plummer, a 29-year old businessman and Navy Reserve officer, ran as the GOP's candidate for Lieutenant Governor in 2010. He works in his family's lumber business. Plummer is calling on government to foster a better job growth market.
Tuesday night during a victory party at the Regency Center in O'Fallon Plummer said the 12th district has been, "decimated by poor public policy," and he promised the Republican party would change that in November.
" I am a fiscal conservative and a social conservative," Plummer said predicting he will match up well with southern Illinois voters.
The 12th Congressional District includes part of Madison County and all of eleven other counties including St. Clair and Monroe Counties.