Based on per capita income, one of the more reliable measures of affluence, Sudden Valley ranks 97th of 522 areas in the state of Washington to be ranked.
According to the United States Census Bureau, the CDP has a total area of 8.1 square miles (21.0 km²), of which, 6.2 square miles (16.1 km²) of it is land and 1.9 square miles (4.8 km²) of it (22.99%) is water.
There were 1,675 households out of which 31.4% had children under the age of 18 living with them, 61.5% were married couples living together, 6.1% had a female householder with no husband present, and 29.2% were non-families. 20.7% of all households were made up of individuals and 4.9% had someone living alone who was 65 years of age or older. The average household size was 2.49 and the average family size was 2.87.
In the CDP the population was spread out with 23.5% under the age of 18, 8.2% from 18 to 24, 30.5% from 25 to 44, 28.3% from 45 to 64, and 9.6% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 105.7 males. For every 100 females age 18 and over, there were 102.2 males.
The median income for a household in the CDP was $51,843, and the median income for a family was $60,250. Males had a median income of $45,568 versus $33,565 for females. The per capita income for the CDP was $24,563. About 4.3% of families and 6.4% of the population were below the poverty line, including 6.0% of those under age 18 and 4.0% of those age 65 or over.