Peoria, city, seat (1825) of Peoria county, centralIllinois, U.S. Peoria lies along theIllinois Riverwhere it widens to form Peoria Lake, about 160 miles (260 km) southwest ofChicago. With Peoria Heights, West Peoria, Bartonville,Bellevue, East Peoria, Creve Coeur, Marquette Heights, North...