Brighton is a home rule municipality city located in Adams and Weld counties, Colorado, United States. Brighton is the county seat of Ada…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.