Rock Island is a city in Rock Island County, Illinois, United States. The population was 39,684 at the 2000 census. It is the county seat of Rock Island County and is one of the Quad Cities, along with neighboring Moline and the Iowa cities of Davenport and Bettendorf. The original Rock Island, from which the city gets its name, is the largest island in the Mississippi river and is now known as Arsenal Island. Rock Island apartments for rent comparison page shows most up to date rent information on Rock Island apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.