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.

The Rock River is a tributary of the Mississippi River, approximately 299 miles (481 km) long, in the U.S. states of Wisconsin and Illinois. The river was known as the Sinnissippi to Sauk and Meskwaki peoples; the name means "rocky waters".