Peoria, Illinois is the county seat of Peoria County. It's home to Caterpillar Tractor, Richard Pryor, and the late Sam Kinison. The population is somewhere around 120,000. (More information about Peoria is available.)
Pekin, Illinois is the county seat of Tazewell County. Its population is about 30,000. Pekin's main claim to fame is that it is the birthplace of United States Senator Everett McKinley Dirksen, possibly one of the greatest orators that body has ever known.