Thornton, city, Adams County, northern Colorado, near Denver; incorporated 1956. Primarily a residential city, it has some light industry. The area was settled by ranchers in the late 19th century, but the community was not platted until the early 1950s. It is named for Dan Thornton, governor of Colorado from 1951 to 1955. Population 40,343 (1980); 55,031 (1990); 82,384 (2000).
