As of the census of 2000, there were 394,542 people, 130,403 households, and 97,411 families residing in the county. The population density was 476 people per square mile (184/km²). There were 134,513 housing units at an average density of 162 per square mile (63/km²). The racial makeup of the county was 56.37% White, 14.91% Black or African American, 0.79% Native American, 12.75% Asian, 0.78% Pacific Islander, 8.01% from other races, and 6.39% from two or more races. 17.64% of the population were Hispanic or Latino of any race. 8.5% were of German, 6.4% Irish and 6.0% English ancestry according to Census 2000. 75.7% spoke English, 12.1% Spanish and 6.6% Tagalog as their first language.
There were 130,403 households out of which 39.90% had children under the age of 18 living with them, 55.70% were married couples living together, 13.80% had a female householder with no husband present, and 25.30% were non-families. 19.60% of all households were made up of individuals and 6.50% had someone living alone who was 65 years of age or older. The average household size was 2.90 and the average family size was 3.33.
In the county the population was spread out with 28.30% under the age of 18, 9.20% from 18 to 24, 31.30% from 25 to 44, 21.70% from 45 to 64, and 9.50% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 101.50 males. For every 100 females age 18 and over, there were 100.20 males.
The median income for a household in the county was $54,099, and the median income for a family was $60,597. Males had a median income of $41,787 versus $31,916 for females. The per capita income for the county was $21,731. About 6.10% of families and 8.30% of the population were below the poverty line, including 10.30% of those under age 18 and 6.30% of those age 65 or over.
Solano County is served by several transit agencies:
Each agency interconnects with each other, enabling transit trips throughout the county. Service also connects with BART stations in Contra Costa County. Transit links are provided to Napa, Yolo and Sacramento counties as well.
Greyhound and Amtrak provide long-distance intercity service.
General aviation airports in Solano County which are open to the public are the Nut Tree Airport and Rio Vista Municipal Airport.