In the Nebraska license plate system, Platte County is represented by the prefix 10 (it had the tenth-largest number of vehicles registered in the county when the license plate system was established in 1922).
1860 - 782 1870 - 1,899 1880 - 9,511 1890 - 15,437 1900 - 17,747 1910 - 19,006 1920 - 19,464 1930 - 21,181 1940 - 20,191 1950 - 19,910 1960 - 23,992 1970 - 26,508 1980 - 28,852 1990 - 29,820 2000 - 31,662
As of the census of 2000, there were 31,662 people, 12,076 households, and 8,465 families residing in the county. The population density was 47 people per square mile (18/km²). There were 12,916 housing units at an average density of 19 per square mile (7/km²). The racial makeup of the county was 94.29% White, 0.35% Black or African American, 0.28% Native American, 0.40% Asian, 0.03% Pacific Islander, 3.49% from other races, and 1.15% from two or more races. 6.54% of the population were Hispanic or Latino of any race.
There were 12,076 households out of which 36.10% had children under the age of 18 living with them, 59.20% were married couples living together, 7.60% had a female householder with no husband present, and 29.90% were non-families. 25.90% of all households were made up of individuals and 11.40% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 3.14.
In the county the population was spread out with 29.00% under the age of 18, 8.10% from 18 to 24, 27.50% from 25 to 44, 21.60% from 45 to 64, and 13.80% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 98.40 males. For every 100 females age 18 and over, there were 95.60 males.
The median income for a household in the county was $39,359, and the median income for a family was $47,776. Males had a median income of $30,672 versus $21,842 for females. The per capita income for the county was $18,064. About 5.40% of families and 7.70% of the population were below the poverty line, including 9.00% of those under age 18 and 6.80% of those age 65 or over.