Collinsville is a city located mainly in Madison County, and partially in St. Clair County, both in Illinois. As of the 2010 census, the city had a population of 26,016. Collinsville is approximately 12 miles from St. Louis, Missouri and is considered part of that city's Metro-East area. Famously, it is the home of the Brooks Catsup Bottle Water Tower; the world's largest ketchup bottle—and is the world's horseradish capital. Monks Mound, the largest man-made earthwork in the North America, and now part of the Cahokia Mounds State Historic Site, is located here.