[4] According to the United States Census Bureau, the city has a total area of 1.96 square miles (5.08 km2), all land.

He operated a rock quarry, and constructed a tavern, a barbershop, a grocery store, and a blacksmith shop.

Due to Madden's prominence in the community, the town was then named Maddenville.

With a location on the Manchester Trail, a route that was mostly frequented by mail coaches and prairie schooners going west, Maddenville in the 1800s became a prosperous town on the outskirts of St. Louis, to which it was connected by a streetcar line.

In 1919, it was discovered by the residents of Maddenville that the inhabitants of the neighboring Maplewood were planning to elect whether or not to annex their town.

To avoid annexation and to establish their own school district, the residents decided to incorporate Maddenville into a village.

During the late 1920s, the village earned an unhealthy reputation for its numerous gambling houses and illegal activities that took place around the intersection of Manchester Road and Brentwood Boulevard.

The first mayor, James L. Willingham (in office from 1929 to 1931), ran on the promise to clean Brentwood up and eliminate the casinos, along with the hoodlums who hung around them, which he did.

On April 12, 1929, Willingham signed ordinance 1A, which established Brentwood as a city and determined its boundaries.

[6] The 2020 United States census[8] counted 8,233 people, 4,044 households, and 1,785 families in Brentwood.

Brentwood is served by the Blue Line of the St. Louis region's MetroLink light rail system.

It connects the Brentwood I-64 light rail station with MetroBus routes and paratransit services.