As of the 2000 census, there were 28,051 people, 9,785 households, and 7,338 families residing in the city. The population density was 4,965.4 people per square mile (1,916.9/km²). There were 10,022 housing units at an average density of 1,774.0/sq mi (684.9/km²). The racial makeup of the city was 90.38% White, 3.64% African American, 0.15% Native American, 2.65% Asian, 0.01% Pacific Islander, 1.67% from other races, and 1.49% from two or more races. Hispanic or Latino of any race were 5.86% of the population.
The top five ancestries reported in Oak Forest as of the 2000 census were Irish (26.3 %), German (25.1 %), Polish (18.3 %), Italian (13.0 %) and Dutch (5.1 %).
There were 9,785 households out of which 36.9 % had children under the age of 18 living with them, 61.0 % were married couples living together, 9.7 % had a female householder with no husband present, and 25.0 % were non-families. 20.7 % of all households were made up of individuals and 5.9 % had someone living alone who was 65 years of age or older. The average household size was 2.81 and the average family size was 3.30.
In the city the population was spread out with 26.0 % under the age of 18, 9.1 % from 18 to 24, 31.0 % from 25 to 44, 24.7 % from 45 to 64, and 9.2 % who were 65 years of age or older. The median age was 36 years. For every 100 females there were 99.3 males. For every 100 females age 18 and over, there were 97.7 males.
The median income for a household in the city was $60,073, and the median income for a family was $68,862. Males had a median income of $48,808 versus $30,137 for females. The per capita income for the city was $23,487. About 2.7 % of families and 3.6 % of the population were below the poverty line, including 3.1 % of those under age 18 and 3.4 % of those age 65 or over.
Oak Forest is served by U.S. Route 6 (159th Street), Illinois Route 50 (Cicero Avenue). Central Avenue serves as a sort of Main Street for Oak Forest, where the local Jewel, Post Office, Acorn Public Library, Oak Forest Park District, Police Station/Fire Department/City Hall, and Oak Forest High School are all located.
Nearby Interstate 57 serves Oak Forest, just north of its intersection with Interstate 80. It a close drive south to the I-57 interchange at 167th Street and Cicero Avenue or east to the interchange at 159th Street (U.S. Route 6) and Pulaski Road/Crawford Avenue. The Tri-State Tollway (I-294) is also accessible within a few miles of Oak Forest.
Pace (transit) bus route 354 runs from Harvey down 147th and Central Avenue through Oak Forest to Tinley Park. Pace bus route 364 runs from Hammond, Indiana to Orland Square Mall in Orland Park down 159th Street (U.S. Route 6) through Oak Forest and other south suburbs. Pace bus route 383 runs down Cicero Avenue (Illinois Route 50) from Chicago Midway International Airport in the south side of Chicago to 159th Street at Oak Forest Hospital.
The Oak Forest station of the Metra commuter rail line, located at 159th and Cicero, is a popular option for commuters to Chicago. This station is part of the Rock Island District Metra line that runs between Joliet, IL and the LaSalle Street Station in the Chicago Loop.