As of the census of 2000, there were 29,736 people, 10,332 households, and 7,501 families residing in the county. The population density was 16 people per square mile (6/km²). There were 17,489 housing units at an average density of 9 per square mile (4/km²). The racial makeup of the county was 91.80% White, 0.24% Black or African American, 0.31% Native American, 0.96% Asian, 0.04% Pacific Islander, 5.43% from other races, and 1.21% from two or more races. 8.09% of the population were Hispanic or Latino of any race.
There were 10,332 households out of which 40.80% had children under the age of 18 living with them, 63.50% were married couples living together, 6.20% had a female householder with no husband present, and 27.40% were non-families. 18.40% of all households were made up of individuals and 3.20% had someone living alone who was 65 years of age or older. The average household size was 2.87 and the average family size was 3.30.
The median income for a household in the county was $64,962, and the median income for a family was $72,510. Males had a median income of $47,236 versus $28,621 for females. The per capita income for the county was $33,767. Only 42.9% are natives of Utah. 5.40% of the population and 3.00% of families were below the poverty line.
According to a 2000 survey by the Association of Statisticians of American Religious Bodies, Summit County is much more diverse in religious belief than Utah as a whole. Fully two in five people (44.2%) of the population claim no religion at all while among those that do, The Church of Jesus Christ of Latter-day Saints (Mormons) make up the largest group at 36.8% (compared with some 66% statewide), followed by Roman Catholics at 10.6%.