Lake Forest is located in the North Shore area, at 42°14′5″N 87°51′3″W (42.234788, -87.851042).
According to the 2010 census, the city has a total area of 17.24 square miles (44.7 km2), of which 17.18 square miles (44.5 km2) (or 99.65%) is land and 0.07 square miles (0.18 km2) (or 0.41%) is water.
As Lake Forest was first developed in 1857, the planners laid roads that would provide very limited access to the city in an effort to prevent outside traffic and further isolate the tranquil settlement from neighboring areas. Though considerably more accessible today, due in part to the extensive new construction taking place further west, the much smaller neighborhood of eastern Lake Forest, near the coast of Lake Michigan, remains relatively secluded and is one of the most scenic, historical, and architecturally significant suburbs of Chicago. These neighborhoods include estates and homes designed by distinguished architects like Howard Van Doren Shaw, David Adler, Frank Lloyd Wright, Arthur Heun, Jerome Cerny, Henry Ives Cobb, and modernist George Fred Keck among others. Landscape architects Frederick Law Olmsted and Jens Jensen also designed projects in Lake Forest. Market Square, designed by Howard Van Doren Shaw, was completed in 1916 as a commercial center for Lake Forest.