Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Peoria County is a county located in the U.S. state of Illinois. As of 2006, the population was 182,495. Its county seat is Peoria, Illinois. Peoria County is part of the Peoria, Illinois, Metropolitan Statistical Area. According to the U.S. Census Bureau, the county has a total area of 631 square miles (1,634 km²), of which 620 square miles (1,605 km²) is land and 11 square miles (29 km²) (1.80%) is water.