Adams County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 519,572. The county seat is Brighton, and the largest city is Thornton. The county is named for Alva Adams, an early Governor of the State of Colorado in 1887–1889. Adams County is part of the Denver–Aurora–Lakewood, CO Metropolitan Statistical Area.

Brighton is a home rule municipality city located in Adams and Weld counties, Colorado, United States. Brighton is the county seat of Adams County and a part of the Denver–Aurora–Lakewood, CO Metropolitan Statistical Area and the Front Range Urban Corridor. The city population was 40,083 at the 2020 United States Census with 39,718 residing in Adams County and 365 residing in Weld County.