At one time, the large JA Ranch, founded by Charles Goodnight and John George Adair, which reached into six counties, held acreage in Randall County.
As of the census of 2000, there were 104,312 people, 41,240 households, and 28,785 families residing in the county. The population density was 114 people per square mile (44/km²). There were 43,261 housing units at an average density of 47 per square mile (18/km²). The racial makeup of the county was 90.44% White, 1.50% Black or African American, 0.65% Native American, 1.03% Asian, 0.03% Pacific Islander, 4.71% from other races, and 1.64% from two or more races. 10.27% of the population were Hispanic or Latino of any race.
There were 41,240 households out of which 33.90% had children under the age of 18 living with them, 57.50% were married couples living together, 9.20% had a female householder with no husband present, and 30.20% were non-families. 25.40% of all households were made up of individuals and 8.50% had someone living alone who was 65 years of age or older. The average household size was 2.49 and the average family size was 3.00.
In the county, the population was spread out with 26.10% under the age of 18, 11.20% from 18 to 24, 28.40% from 25 to 44, 22.40% from 45 to 64, and 11.90% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 94.70 males. For every 100 females age 18 and over, there were 91.20 males.
The median income for a household in the county was $42,712, and the median income for a family was $52,420. Males had a median income of $36,333 versus $25,358 for females. The per capita income for the county was $21,840. About 5.70% of families and 8.10% of the population were below the poverty line, including 8.50% of those under age 18 and 6.60% of those age 65 or over.