Old Mill Creek is a village in Lake County, Illinois, United States. The population was 178 at the 2010 census.
Old Mill Creek is located at 42°25′19″N 87°58′57″W (42.421820, -87.982511).
According to the 2010 census, Old Mill Creek has a total area of 10.804 square miles (27.98 km2), of which 10.63 square miles (27.53 km2) (or 98.39%) is land and 0.174 square miles (0.45 km2) (or 1.61%) is water.
As of the census of 2000, there were 251 people, 98 households, and 68 families residing in the village. The population density was 24.8 people per square mile (9.6/km2). There were 104 housing units at an average density of 10.3 per square mile (4.0/km2). The racial makeup of the village was 87.25% White, 2.39% African American, 6.37% Asian, 1.20% from other races, and 2.79% from two or more races. Hispanic or Latino of any race were 2.39% of the population.
There were 98 households, out of which 31.6% had children under the age of 18 living with them, 61.2% were married couples living together, 6.1% had a female householder with no husband present, and 29.6% were non-families. 23.5% of all households were made up of individuals, and 5.1% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.09.
In the village, the population was spread out, with 23.9% under the age of 18, 6.0% from 18 to 24, 35.5% from 25 to 44, 27.5% from 45 to 64, and 7.2% who were 65 years of age or older.