Mountain Brook is a city in southeastern Jefferson County, Alabama, United States, and a suburb of Birmingham. Its population at the 2020 census was 22,461.

Jefferson County is the most populous county in the U.S. state of Alabama, located in the central portion of the state. As of the 2020 census, its population was 674,721. Its county seat is Birmingham. Its rapid growth as an industrial city in the 20th century, based on heavy manufacturing in steel and iron, established its dominance. Jefferson County is the central county of the Birmingham-Hoover, AL Metropolitan Statistical Area.