Solano County was one of the original counties of California, created in 1850 at the time of statehood.
According to the U.S. Census Bureau, the county has a total area of 2,348 km² (907 mi²). 2,148 km² (829 mi²) of it is land and 201 km² (77 mi²) of it is water. The total area is 8.55% water.
As of the census2 of 2000, there are 394,542 people, 130,403 households, and 97,411 families residing in the county. The population density is 184/km² (476/mi²). There are 134,513 housing units at an average density of 63/km² (162/mi²). The racial makeup of the county is 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 are Hispanic or Latino of any race.
There are 130,403 households out of which 39.90% have children under the age of 18 living with them, 55.70% are married couples living together, 13.80% have a female householder with no husband present, and 25.30% are non-families. 19.60% of all households are made up of individuals and 6.50% have someone living alone who is 65 years of age or older. The average household size is 2.90 and the average family size is 3.33.
In the county the population is 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 are 65 years of age or older. The median age is 34 years. For every 100 females there are 101.50 males. For every 100 females age 18 and over, there are 100.20 males.
The median income for a household in the county is $54,099, and the median income for a family is $60,597. Males have a median income of $41,787 versus $31,916 for females. The per capita income for the county is $21,731. 8.30% of the population and 6.10% of families are below the poverty line. Out of the total people living in poverty, 10.30% are under the age of 18 and 6.30% are 65 or older.