Freeburg, IL. Freeburg is a village in St. Clair County, Illinois, United States. As of 2010, Freeburg had a population of 4,354. Freeburg lies in the fertile and rolling southern Illinois plains between the Kaskaskia and Mississippi Rivers. It was platted in 1836 as the town of Urbana by immigrants to this area from Virginia around 1800. The first European settlers of Freeburg were of English and Irish ancestry.