Oak Park is located immediately west of Chicago, at 41° 53’ 6” north latitude, 87° 47’ 3” west longitude. The boundary between Oak Park and Chicago is Austin Boulevard on the east side of Oak Park and North Avenue on the north side. Along its southern border on Roosevelt Road Oak Park borders Cicero from Austin to Lombard Avenue, and Berwyn from Lombard to Harlem Avenue. On its west, Oak Park borders Forest Park along Harlem between Roosevelt and South Boulevard, and River Forest between North Boulevard and North Avenue. The total land area of Oak Park is approximately 4.7 square miles. The entire Village of Oak Park lies on the shore of the ancient Lake Chicago, which covered most of the city of Chicago during the last Ice Age and is today called Lake Michigan. Ridgeland Avenue in eastern Oak Park marks the shoreline of the ancient lake, and was once an actual ridge. One of North America’s four continental divides runs through Oak Park, approximately from North and Ridgeland avenues, through Taylor Park at Division Street, to Scoville Park at Lake Street, where it veers west to Harlem Avenue. This divide separates the St. Lawrence River watershed from the Mississippi River watershed.