Oak Park, Illinois is a suburb bordering the west side of the City of Chicago in Cook County, Illinois, United States. It is the twenty-fifth largest city in Illinois. Oak Park has easy access to downtown Chicago (the Chicago Loop) thanks to public transportation such as the Chicago 'L' Blue and Green lines, CTA buses, and Metra commuter rail. As of the 2000 census, the area had a total population of 52,524. A census estimate for 2003 showed that the population had dipped to 50,824.