As of the 2000 census, Yolo County had a population of 168,660. Excluding the conurbation of the University of California, Davis and the surrounding City of Davis, and the neighboring City of Sacramento, Yolo County remains a relatively rural agricultural region. This is evidenced by the multi-billion dollar California tomato industry, centering around Yolo County, dominating 90% of the tomato market in the United States.
Yolo County is part of the Sacramento–Arden-Arcade–Roseville Metropolitan Statistical Area.
As of the census of 2000, there were 168,660 people, 59,375 households, and 37,465 families residing in the county. The population density was 166 people per square mile (64/km²). There were 61,587 housing units at an average density of 61 per square mile (23/km²). The racial makeup of the county was 67.67% White, 2.03% Black or African American, 1.16% Native American, 9.85% Asian, 0.30% Pacific Islander, 13.76% from other races, and 5.23% from two or more races. 25.91% of the population were Hispanic or Latino of any race. 10.0% were of German, 6.6% English and 6.4% Irish ancestry according to Census 2000. 68.5% spoke English, 19.5% Spanish, 2.1% Chinese or Mandarin and 1.8% Russian as their first language.
There were 59,375 households out of which 33.6% had children under the age of 18 living with them, 47.6% were married couples living together, 11.1% had a female householder with no husband present, and 36.9% were non-families. 23.3% of all households were made up of individuals and 7.3% had someone living alone who was 65 years of age or older. The average household size was 2.71 and the average family size was 3.25.
In the county the population was spread out with 25.2% under the age of 18, 18.3% from 18 to 24, 28.2% from 25 to 44, 18.9% from 45 to 64, and 9.4% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 95.6 males. For every 100 females age 18 and over, there were 92.2 males.
The median income for a household in the county was $40,769, and the median income for a family was $51,623. Males had a median income of $38,022 versus $30,687 for females. The per capita income for the county was $19,365. About 9.5% of families and 18.4% of the population were below the poverty line, including 16.0% of those under age 18 and 7.4% of those age 65 or over.
Yolo County is made of a system of County Roads. County Roads that begin to be in urban areas are renamed. Some examples include County Road 101 in Woodland being renamed Pioneer Ave. Another example is County Road 102 in Davis being named Pole Line Road.
The numbering system works in the following way:
Each integer road number is one mile apart.