Long Lake is a census-designated place (CDP) in Lake County, Illinois, United States. The population was 3,515 at the 2010 census.
According to the United States Census Bureau, the CDP has a total area of 1.7 square miles (4.4 km), of which 1.0 square mile (2.6 km) is land and 0.6 square miles (1.6 km) (36.75%) is water.
As of the census of 2000, there were 3,356 people, 1,150 households, and 857 families residing in the CDP. The population density was 3,193.3 people per square mile (1,234.1/km²). There were 1,237 housing units at an average density of 1,177.0/sq mi (454.9/km²). The racial makeup of the CDP was 93.33% White, 0.33% African American, 0.33% Native American, 0.72% Asian, 4.41% from other races, and 0.89% from two or more races. Hispanic or Latino of any race were 11.53% of the population.
There were 1,150 households out of which 40.1% had children under the age of 18 living with them, 59.0% were married couples living together, 10.0% had a female householder with no husband present, and 25.4% were non-families. 18.7% of all households were made up of individuals and 4.8% had someone living alone who was 65 years of age or older. The average household size was 2.92 and the average family size was 3.33.
In the CDP, the population was spread out with 30.2% under the age of 18, 8.3% from 18 to 24, 35.5% from 25 to 44, 19.3% from 45 to 64, and 6.8% who were 65 years of age or older. The median age was 33 years. For every 100 females, there were 108.7 males. For every 100 females age 18 and over, there were 105.4 males.
The median income for a household in the CDP was $57,179, and the median income for a family was $61,378. Males had a median income of $41,875 versus $29,919 for females. The per capita income for the CDP was $21,034. About 2.0% of families and 3.8% of the population were below the poverty line, including 2.4% of those under age 18 and 19.6% of those age 65 or over.