Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Peoria is a census-designated place (CDP) in Arapahoe County, Colorado, United States. The population as of the 2010 Census was 163. Arapahoe County is the third most populous of the 64 counties of the state of Colorado of the United States. The United States Census Bureau estimated that the county population was 572,003 in 2010 census, a 17.2% increase since 2000 census. The county seat is Littleton; the most populous city is Aurora. Arapahoe County is part of the Denver-Aurora Metropolitan Statistical Area and the Denver-Aurora-Boulder Combined Statistical Area. Arapahoe County calls itself "Colorado's First County" since its origins predate the Pike's Peak Gold Rush.