Lake Forest is a city located in Lake County, Illinois, United States. Per the 2020 census, the population was 19,367. The city is along the shore of Lake Michigan, and is a part of the Chicago metropolitan area and the North Shore. Lake Forest was founded with Lake Forest College and was laid out as a town in 1857, a stop for travelers making their way south to Chicago. The Lake Forest City Hall, designed by Charles Sumner Frost, was completed in 1898. It originally housed the fire department, the Lake Forest Library, and city offices.

Lake County is situated in the northeastern corner of the U.S. state of Illinois, along the shores of Lake Michigan. As of the 2020 census, it has a population of 714,342, making it the third-most populous county in Illinois. Its county seat is Waukegan, the tenth-largest city in Illinois. The county is primarily suburban, with some urban areas and some rural areas. Due to its location, immediately north of Cook County, Lake County is one of the collar counties of the Chicago metropolitan area. Its northern boundary is the Wisconsin state line.