As of the census of 2000, there were 365,196 people, 139,572 households, and 97,281 families residing in the county. The U.S. Census Bureau estimates that the population of the County has grown to 394,878 by 2003. Current 2008 estimates put the population at more than 407,000. The population density was 1,185 people per square mile (458/km²). There were 147,079 housing units at an average density of 477 per square mile (184/km²). The racial makeup of the county was 82.41% White, 9.52% Black or African American, 0.30% Native American, 2.50% Asian, 0.04% Pacific Islander, 3.06% from other races, and 2.18% from two or more races. 11.15% of the population were Hispanic or Latino of any race.
There were 139,572 households out of which 33.90% had children under the age of 18 living with them, 54.30% were married couples living together, 11.50% had a female householder with no husband present, and 30.30% were non-families. 22.90% of all households were made up of individuals and 6.60% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 3.07. The Department of Education states that in 2003, school enrollment was approximately 72,630. As of 2006, the Seminole County School District was the 52nd largest in the nation.
In the county the population was spread out with 25.40% under the age of 18, 8.40% from 18 to 24, 32.00% from 25 to 44, 23.60% from 45 to 64, and 10.60% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 95.90 males. For every 100 females age 18 and over, there were 92.90 males.
The median income for a household in the county was $49,326, and the median income for a family was $56,895. Males had a median income of $40,001 versus $28,217 for females. The per capita income for the county was $24,591. About 5.10% of families and 7.40% of the population were below the poverty line, including 8.60% of those under age 18 and 6.60% of those age 65 or over. As of March 2009, according to Workforce Central Florida, the unemployment rate for Seminole County is 9.2 percent.
Because of the massive urban sprawl in the area and outdated and unplanned transit infrastructure, traffic congestion is a growing concern. Fundamentally, the lack of east-west mobility in the area creates severe traffic issues every weekday. Many residents of Seminole County work in Orange County, and those in northern Volusia County commute through Seminole County daily to Orange County.