Brentwood is a borough in Allegheny County, Pennsylvania, United States. The population was 10,082 at the 2020 census. It is a residential suburb of the Pittsburgh metropolitan area. Brentwood, located approximately 6 miles from downtown Pittsburgh and is 101 years old, was once an integral part of Baldwin Township, which included the villages of Brentwood, …Brentwood is a borough in Allegheny County, Pennsylvania, United States. The population was 10,082 at the 2020 census. It is a residential suburb of the Pittsburgh metropolitan area. Brentwood, located approximately 6 miles from downtown Pittsburgh and is 101 years old, was once an integral part of Baldwin Township, which included the villages of Brentwood, Point View, and Whitehall.