Rock Island is a city in and the county seat of Rock Island County, Illinois, United States. The population was 37,108 at the 2020 census. Located at the confluence of the Rock and Mississippi rivers, it is one of the Quad Cities along with neighboring Moline and East Moline in Illinois and the cities of Davenport and Bettendorf in Iowa. The Quad Cities had a population of 384,324 in 2020.