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. The city is home to Rock Island Arsenal, the largest government-owned weapons manufacturing arsenal in the US, which employs 6,000 people. The original Rock Island, from which the city name is derived, is now called Arsenal Island.

Rock Island County is a county located in the U.S. state of Illinois, bounded on the west by the Mississippi River. According to the 2020 census, it had a population of 144,672. Its county seat is Rock Island; its largest city is neighboring Moline. Rock Island County is one of the four counties that make up the Davenport-Moline-Rock Island, IA-IL Metropolitan Statistical Area.