page_title: Cook County, Illinois
section_title: Adjacent counties
hierarchical_section_title: Cook County, Illinois / Communities / Adjacent counties
caption_attribution_description: Chicago metro area from an altitude of 223 nautical miles (413 km), 02:01:49 AM CDT, October 9, 2013, ISS Expedition 37
context_page_description: Cook County is the most populous county in the U.S. state of Illinois and the second-most-populous county in the United States after Los Angeles County, California. As of 2019, the population was 5,150,233. Its county seat is Chicago, the most populous city in Illinois and the third-most-populous city in the United States. More than 40% of all residents of Illinois live in Cook County.
  Cook County was incorporated in 1831 and named for Daniel Pope Cook, an early Illinois statesman, although there is no record of Cook having ever visited the area. It achieved its present boundaries in 1839. During the first half of the 20th century it had the absolute majority of Illinois's population.
  There are 134 municipalities located partially or wholly within Cook County, the largest of which is Chicago, home to approximately 54% of the county's population. The part of the county outside of the Chicago and Evanston city limits is divided into 29 townships; these often divide or share governmental services with local municipalities. Townships within Chicago were abolished in 1902 but are retained for real estate assessment purposes.
context_section_description: McHenry County, Illinois – northwest
  Lake County, Illinois – north
  Berrien County, Michigan – east
  Lake County, Indiana – southeast
  Will County, Illinois – south
  DuPage County, Illinois – west
  Kane County, Illinois – west
caption: Cook County and adjacent counties, from ISS Expedition 37 in 2013.
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