Umatilla County is part of the Pendleton–Hermiston Micropolitan Statistical Area.
As of the census of 2000, there were 70,548 people, 25,195 households, and 17,838 families residing in the county. The population density was 22 people per square mile (8/km²). There were 27,676 housing units at an average density of 9 per square mile (3/km²). The racial makeup of the county was 82.00% White, 0.82% Black or African American, 3.37% Native American, 0.75% Asian, 0.18% Pacific Islander, 10.67% from other races, and 2.21% from two or more races. 16.11% of the population were Hispanic or Latino of any race. 17.1% were of German, 13.0% American, 9.8% English and 6.8% Irish ancestry according to Census 2000. 84.4% spoke English and 14.3% Spanish as their first language.
There were 25,195 households out of which 35.00% had children under the age of 18 living with them, 55.10% were married couples living together, 10.60% had a female householder with no husband present, and 29.20% were non-families. 23.70% of all households were made up of individuals and 9.70% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.14.
In the county, the population was spread out with 27.80% under the age of 18, 9.40% from 18 to 24, 28.30% from 25 to 44, 22.20% from 45 to 64, and 12.30% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 104.80 males. For every 100 females age 18 and over, there were 104.70 males.
The median income for a household in the county was $36,249, and the median income for a family was $41,850. Males had a median income of $31,479 versus $22,325 for females. The per capita income for the county was $16,410. About 9.80% of families and 12.70% of the population were below the poverty line, including 16.20% of those under age 18 and 8.70% of those age 65 or over.