In 1844, the area was established as Thompson Station and Suffolk Station, two new stations on the expansion of the mainline of the Long Island Rail Road.

On March 21, 1851, it became the utopian community named Modern Times. The colony was established on 750 acres (3.0 km²) of land by Josiah Warren and Stephen Pearl Andrews. In 1864, it was renamed Brentwood after the town of Brentwood, Essex, in England.

By contract, all the land in the colony was bought and sold at cost, with 3 acres (12,000 m²) being the maximum allowable lot size. The community was said to be based on the idea of individual sovereignty and individual responsibility. Individuals were encouraged to pursue their self-interest as they saw fit. All products of labor were considered private property. The community had a local private currency based upon labor exchange in order to trade goods and services (see Mutualism (economic theory)). All land was private property, with the exception of alleys which were initially considered common property but later converted to private property. Initially, no system of authority existed in the colony; there were no courts, jails or police. This appears to have given some credence to Warren's theories that the most significant cause of violence in society was most attributable to policies and law which did not allow complete individuality in person and property. However, the modest population of the colony might be considered a factor in this characteristic. The Civil War, as well as new residents that did not share the colony's philosophy, are said to have contributed to its eventual dissolution. Almost all of the original buildings that existed in Modern Times have been destroyed, aside from two Octagon houses,^{[where? — see talk page]}the original schoolhouse and a residence.

During the first half of the 20th century, Brentwood was home to the Ross Health Resort Onehtah, managed by Dr. William H. Ross. Onehtah was a place where a person could escape the pollution of the city. It was thought that the smell of pine needles brought a person good health.

Brentwood is the site of Pilgrim State Hospital (once one of the world's largest hospitals and psychiatric institutions), now known as Pilgrim Psychiatric Center. A 52-acre (0.21 km²) portion of the psychiatric center was converted into the Brentwood State Park athletic field complex, which officially opened in 2009.

Brentwood's Centennial Celebration was on June 16–17, 1950. The 150th anniversary of the community was commemorated on May 9–11, 2007.

Brentwood High School has a nationally recognized boys soccer team that won national championship in 2019.

Brentwood is located at 40°46′54″N 73°14′39″W / 40.78167°N 73.24417°W / 40.78167; -73.24417 (40.781805, −73.244060).

According to the United States Census Bureau, the CDP has a total area of 10.1 square miles (26.1 km²).^{[citation needed]}

As of the census of 2010, there were 60,664 people, 12,580 households, and 10,894 families residing in the CDP. The population density was 6028 per square mile (2,069.3/km²). There were 13,039 housing units at an average density of 1,295.6/sq mi (500.4/km²). The racial makeup of the CDP was 18.6% White, 16.3% African American, 0.5% Native American, 1.9% Asian, 0.11% Pacific Islander, and 5.7% from two or more races. Hispanic or Latino of any race were 64.3% of the population.

There were 12,580 households, out of which 46.6% had children under the age of 18 living with them, 61.2% were married couples living together, 17.4% had a female householder with no husband present, and 13.4% were non-families. 9.5% of all households were made up of individuals, and 4.4% had someone living alone who was 65 years of age or older. The average household size was 4.23 and the average family size was 4.19.

In the CDP, the population was spread out, with 29.9% under the age of 18, 10.6% from 18 to 24, 32.8% from 25 to 44, 18.5% from 45 to 64, and 8.2% who were 65 years of age or older. The median age was 31 years. For every 100 females, there were 100.2 males. For every 100 females age 18 and over, there were 97.5 males.

The median income for a household in the CDP was $68,314, and the median income for a family was $57,047. Males had a median income of $31,022 versus $25,946 for females. The per capita income for the CDP was $15,833. About 7.5% of families and 11.3% of the population were below the poverty line, including 13.7% of those under age 18 and 10.6% of those age 65 or over.

Updated February 12, 2017

Race in Brentwood NY 2015 (City-data.com)