Peoria is the county seat of Peoria County, Illinois, and the largest city on the Illinois River. As of the 2010 census, the city had a population of 115,007. It is the principal city of the Peoria Metropolitan Area in Central Illinois, consisting of the counties of Marshall, Peoria, Stark, Tazewell, and Woodford, which had a population of 373,590 in 2011.