Forest Lake is an unincorporated community and census-designated place (CDP) in Ela Township of Lake County, Illinois, United States. It is about 35 miles (56 km) northwest of downtown Chicago. Per the 2020 census, the population was 1,784. The community was founded in 1935 as a vacation community for Chicago residents.

Forest Lake is located in southwestern Lake County at 42°12′28″N 88°3′13″W / 42.20778°N 88.05361°W / 42.20778; -88.05361 (42.207824, -88.053475). It is bordered to the north, west, and south by Hawthorn Woods, and to the east and south by Kildeer. The village of Lake Zurich boundary comes within 0.1 miles (0.16 km) of the southwest corner of the CDP.

According to the United States Census Bureau, the Forest Lake CDP has a total area of 0.42 square miles (1.1 km), of which 0.35 square miles (0.9 km) are land and 0.1 square miles (0.2 km), or 14.86%, are water, consisting of the community's namesake water body.

Historical population

Census	Pop.	Note	%±
2010	1,659		—
2020	1,784		7.5%
U.S. Decennial Census 2010 2020

Forest Lake CDP, Illinois – Racial and ethnic composition
Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.

Race / Ethnicity (NH = Non-Hispanic)	Pop 2000	Pop 2010	Pop 2020	% 2000	% 2010	% 2020
White alone (NH)	1,412	1,454	1,468	92.29%	87.64%	82.29%
Black or African American alone (NH)	6	17	12	0.39%	1.02%	0.67%
Native American or Alaska Native alone (NH)	0	0	2	0.00%	0.00%	0.11%
Asian alone (NH)	14	63	79	0.92%	3.80%	4.43%
Pacific Islander alone (NH)	0	1	3	0.0%	0.06%	0.17%
Other race alone (NH)	0	1	4	0.00%	0.06%	0.22%
Mixed race or Multiracial (NH)	24	9	80	1.57%	0.54%	4.48%
Hispanic or Latino (any race)	74	114	136	4.84%	6.87%	7.62%
Total	1,530	1,659	1,784	100.00%	100.00%	100.00%

As of the census of 2010, there were 1,659 people, 662 households, and 446 families residing in the CDP. The population density was 3,606.5 inhabitants per square mile (1,392.5/km). There were 662 housing units at an average density of 1,439.1 per square mile (555.6/km). The racial makeup of the CDP in 2016 was 89.6% White, 1.0% African American, 3.6% Asian, 0.12% from other races, and 0.5% from two or more races. Hispanic or Latino of any race were 5.0% of the population. The percentage of people "foreign born" in Forest Lake is 17.4%, with 14.1% born in Europe.

There were 622 households in 2010, out of which 40.1% had children under the age of 18 living with them, 67.7% were married couples living together, 8.2% had a female householder with no husband present, and 20.9% were non-families. 14.2% of all households were made up of individuals, and 3.0% had someone living alone who was 65 years of age or older. The average household size was 2.85 and the average family size was 3.19.

In the 2000 CDP, the population was spread out, with 29.0% under the age of 18, 4.2% from 18 to 24, 34.5% from 25 to 44, 25.6% from 45 to 64, and 6.7% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 100.8 males. For every 100 females age 18 and over, there were 100.0 males.

The median income for a household in 2016 was $89,276. The 2000 CDP listed the median income for a family at $81,035. Males had a median income of $49,375 versus $36,833 for females. The per capita income for the CDP was $28,737. About 2.6% of families and 3.0% of the population were below the poverty line, including none of those under age 18 and 9.0% of those age 65 or over.