As of the 2000 census, there were 129,461 people, 34,418 households, and 26,983 families residing in the county. However, the California Department of Finance estimates that the population had grown 154,434 as of January 1, 2008. The population density based on the 2000 census was 36/km² (93/sq mi). There were 36,563 housing units at an average density of 26 per square mile (10/km²). The racial makeup of the county was 53.68% White, 8.30% Black or African American, 1.68% Native American, 3.07% Asian, 0.19% Pacific Islander, 28.28% from other races, and 4.79% from two or more races. 43.61% of the population were Hispanic or Latino of any race. 7.1% were of Portuguese, 6.2% German, 5.3% Irish and 5.1% American ancestry according to Census 2000. 63.6% spoke English, 30.9% Spanish, 1.4% Tagalog, 1.4% Portuguese and 1.3% Samoan as their first language.
There were 34,418 households out of which 46.4% had children under the age of 18 living with them, 58.0% were married couples living together, 14.3% had a female householder with no husband present, and 21.6% were non-families. 17.0% of all households were made up of individuals and 6.8% had someone living alone who was 65 years of age or older. The average household size was 3.18 and the average family size was 3.56.
In the county the population was spread out with 29.0% under the age of 18, 11.8% from 18 to 24, 35.0% from 25 to 44, 16.8% from 45 to 64, and 7.4% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 134.8 males. For every 100 females age 18 and over, there were 148.8 males. The ratio may be attributed to the presence of three men's state prisons in the county.
Kings Area Rural Transit (KART) operates regularly scheduled fixed route bus service, vanpool service for commuters and Dial-A-Ride (demand response) services throughout Kings County as well as to Fresno.
Amtrak trains stop in Corcoran and Hanford.
Orange Belt Stages provides inter-city bus service to and from Hanford. Connections with Greyhound can be made in Visalia or Paso Robles.
Hanford Municipal Airport is a general aviation airport located just southeast of Hanford. The privately-owned airport in Avenal is the home of the Central California Soaring Club.