Racial and ethnic composition

2020 census

As of the 2020 census, Affton had a population of 20,417. The median age was 41.1 years. 19.0% of residents were under the age of 18 and 19.1% of residents were 65 years of age or older. For every 100 females there were 93.6 males, and for every 100 females age 18 and over there were 90.5 males age 18 and over. ^{[9] [10]}

100.0% of residents lived in urban areas, while 0.0% lived in rural areas. ^[11]

There were 9,187 households in Affton, of which 23.6% had children under the age of 18 living in them. Of all households, 42.4% were married-couple households, 18.9% were households with a male householder and no spouse or partner present, and 31.3% were households with a female householder and no spouse or partner present. About 35.7% of all households were made up of individuals and 15.6% had someone living alone who was 65 years of age or older. ^[9]

There were 9,579 housing units, of which 4.1% were vacant. The homeowner vacancy rate was 1.0% and the rental vacancy rate was 4.7%. ^[9]

2000 census

As of the census ^[3] of 2000, there were 20,535 people, 8,892 households, and 5,655 families residing in the CDP. The population density was 4,480.1 inhabitants per square mile (1,729.8/km²). There were 9,128 housing units at an average density of 1,991.5 per square mile (768.9/km²). The racial makeup of the CDP was 97.62% White, 0.06% Black, 0.01% American Indian, 1.30% Asian, 0.03% Pacific Islander, 0.28% from other races, and 1.13% from two or more races. 1.01% of the population were Hispanic or Latino of any race.

There were 8,892 households, out of which 26.5% had children under the age of 18 living with them, 51.1% were married couples living together, 9.5% had a female householder with no husband present, and 36.4% were non-families. 31.9% of all households were made up of individuals, and 14.0% had someone living alone who was 65 years of age or older. The average household size was 2.31 and the average family size was 2.93.

In the CDP, the population was spread out, with 21.9% under the age of 18, 6.9% from 18 to 24, 30.3% from 25 to 44, 21.4% from 45 to 64, and 19.5% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 89.1 males. For every 100 females age 18 and over, there were 85.0 males.

The median income for a household in the CDP was $43,327, and the median income for a family was $54,881. Males had a median income of $38,141 versus $28,397 for females. The per capita income for the CDP was $22,059. 3.6% of the population and 2.1% of families were below the poverty line. 3.9% of those under the age of 18 and 4.1% of those 65 and older were living below the poverty line.