Pekin is a the county seat of Tazewell County in the U.S. state of Illinois. Located on the Illinois River, Pekin is also the largest city of Tazewell County, and a key part of the Peoria metropolitan area. As of the 2010 census, its population is 34,094. A small portion of the city limits extends into Peoria County. Pekin is the 13th-most populous city in Illinois, outside of the Chicago Metropolitan Area.