Champaign County was organized in 1833, having been previously a part of Vermilion County. The county and county seat were named for Champaign County, Ohio and Urbana, Ohio respectively, the homeplace of the Illinois legislator who sponsored the bill to create the county. The development of the county was greatly furthered by the arrival of the Chicago Branch of the Illinois Central Railroad, and even more by the establishment of the land-grant university.
Later, the county also got an airport and a mass transit district. The northern part of the county experienced an economic and demographic setback with the closing of Chanute Air Training Center in the 1990s. In the 2004 Presidential election, it was one of only 15 of the 102 Illinois counties where John Kerry received a majority of the vote.