Seal Beach is located in the westernmost corner of Orange County. To the northwest, just across the border with Los Angeles County, lies the city of Long Beach and the adjacent San Pedro Bay. To the southeast are Huntington Harbour, a neighborhood of Huntington Beach, and the unincorporated community of Sunset Beach. To the east lie the city of Westminster and the neighborhood of West Garden Grove, part of the city of Garden Grove. To the north lie the unincorporated community of Rossmoor and the city of Los Alamitos.
As of the census of 2000, there were 24,157 people, 13,048 households, and 5,884 families residing in the city. The population density was 810.3/km² (2,099.5/mi²). There were 14,267 housing units at an average density of 478.6/km² (1,240.0/mi²). The racial makeup of the city was 88.91% White, 1.44% African American, 0.30% Native American, 5.74% Asian, 0.18% Pacific Islander, 1.28% from other races, and 2.16% from two or more races. Hispanic or Latino of any race were 6.43% of the population.
There were 13,048 households, out of which 13.8% had children under the age of 18 living with them, 38.2% were married couples living together, 5.3% had a female householder with no husband present, and 54.9% were non-families. 48.8% of all households were made up of individuals and 34.5% had someone living alone who was 65 years of age or older. The average household size was 1.83 and the average family size was 2.65.
In the city the population was spread out with 13.3% under the age of 18, 4.0% from 18 to 24, 21.5% from 25 to 44, 23.7% from 45 to 64, and 37.5% who were 65 years of age or older. The median age was 54 years. For every 100 females there were 78.3 males. For every 100 females age 18 and over, there were 75.4 males.
The median income for a household in the city was $42,079, and the median income for a family was $72,071. Males had a median income of $61,654 versus $41,615 for females. The per capita income for the city was $34,589. About 3.2% of families and 5.5% of the population were below the poverty line, including 6.2% of those under age 18 and 5.3% of those age 65 or over.