Demographics
As of the census of 2000, there were 3,400,578 people, 1,205,516 households, and 834,217 families residing in the county, making it the largest county by population in Texas. The population density was 1,967 people per square mile (759/km²). There were 1,298,130 housing units at an average density of 751 per square mile (290/km²). The racial makeup of the county was 58.73% White, 18.49% Black or African American, 0.45% Native American, 5.14% Asian, 0.06% Pacific Islander, 14.18% from other races, and 2.96% from two or more races. 32.93% of the population were Hispanic or Latino of any race.

In 2006 Harris County had 3,886,207 residents. This represented 14.3% growth since 2000.

2005 saw Harris county with 37.5% of its population Latino. This represented an increase of over 120,000 in the number of Latinos in the county. 5.5% of the population was Asian. African Americans constituted 18.4% of the county's population, representing a slight decline in percentage. It however meant the total number of African-Americans in the county had risen. In 2000 There were 1,205,516 households out of which 37.70% had children under the age of 18 living with them, 50.60% were married couples living together, 13.70% had a female householder with no husband present, and 30.80% were non-families. 25.10% of all households were made up of individuals and 5.30% had someone living alone who was 65 years of age or older. The average household size was 2.79 and the average family size was 3.38.

In the county, the population was spread out with 29.00% under the age of 18, 10.30% from 18 to 24, 33.40% from 25 to 44, 19.80% from 45 to 64, and 7.40% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 99.20 males. For every 100 females age 18 and over, there were 97.00 males.

The median income for a household in the county was $42,598, and the median income for a family was $49,004. Males had a median income of $37,361 versus $28,941 for females. The per capita income for the county was $21,435. About 12.10% of families and 14.97% of the population were below the poverty line, including 19.60% of those under age 18 and 12.20% of those age 65 or over.

Education

Several school districts serve Harris County communities.

• Aldine ISD
• Alief ISD
• Channelview ISD
• Clear Creek ISD
• Crosby ISD
• Cypress-Fairbanks ISD
• Dayton ISD
• Deer Park ISD
• Galena Park ISD
• Goose Creek CISD
• Houston ISD
• Humble ISD
• Katy ISD
• Klein ISD
• La Porte ISD
• North Forest ISD
• Pasadena ISD
• Sheldon ISD
• Spring ISD
• Spring Branch ISD
• Stafford MSD
• Tomball ISD
• Waller ISD

Harris County operates its own public library system, the Harris County Public Library.
In addition, Houston has the Houston Public Library, a city-controlled public library system.
The cities of Baytown, Bellaire, Deer Park, and Pasadena have their own city-controlled libraries.

Transportation
Many areas in Harris County are served by Metropolitan Transit Authority of Harris County, Texas (METRO), a public transportation agency headquartered in Downtown Houston.

Two commercial airports, George Bush Intercontinental Airport and William P. Hobby Airport, are located in Houston and in Harris County.