Rock Island is a city in and the county seat of Rock Island County, Illinois, United States. The population is about 40,000. Located on the Mississippi River, it is one of the Quad Cities, along with neighboring Moline, East Moline, and the Iowa cities of Davenport and Bettendorf. The Quad Cities has a population of about 380,000. The city is home to Rock Island Arsenal, the largest government-owned weapons manufacturing arsenal in the US, which employs 6,000 people.