Some of the cities, towns, and places in Cook County are Alsip, Arlington Heights, Barrington, Barrington Hills, Barrington Township, Bartlett, Bedford Park, Bellwood, Bensenville, Berkeley, Berrien County, Michigan, Berwyn, Berwyn Township, Bloom Township, Blue Island, Bremen Township, Bridgeview, Broadview, Brookfield, Buffalo Grove, Burbank, Burnham, Burr Ridge, Calumet City, Calumet Park, Calumet Township, Central Stickney, Chicago, Chicago Heights, Chicago Ridge, Cicero, Cicero Township, City of Chicago, City of Evanston, Country Club Hills, Countryside, Crestwood, Deer Park, Deerfield, Des Plaines, Dixmoor, Dolton, DuPage County, DuPage County, Illinois, East Dundee, East Hazel Crest, Elgin, Elk Grove Township, Elk Grove Village, Elmhurst, Elmwood Park, Evanston, Evanston Township, Evergreen Park, Flossmoor, Ford Heights, Forest Park, Forest View, Fort Dearborn, Frankfort, Franklin Park, Glencoe, Glenview, Glenwood, Golf, Hanover Park, Hanover Township, Harvey, Harwood Heights, Hazel Crest, Hickory Hills, Hillside, Hines, Hinsdale, Hodgkins, Hoffman Estates, Hometown, Homewood, Hyde Park Township, Indian Head Park, Indian Hill, Inverness, Jefferson Township, Justice, Kane County, Kane County, Illinois, Kenilworth, La Grange, La Grange Highlands, La Grange Park, Lake County, Lake County, Illinois, Lake County, Indiana, Lake Township, Lake View Township, Lansing, Lemont, Lemont Township, Leyden Township, Lincolnwood, Lynwood, Lyons, Lyons Township, Maine Township, Markham, Matteson, Maywood, McCook, McHenry County, Illinois, Melrose Park, Merrionette Park, Midlothian, Morton Grove, Mount Prospect, New Trier Township, Niles, Niles Township, Norridge, North Riverside, North Township, Northbrook, Northfield, Northfield Township, Northlake, Norwood Park Township, Nottingham Park, Oak Brook, Oak Forest, Oak Lawn, Oak Park, Oak Park Township, Olympia Fields, Orchard Place, Orland Hills, Orland Park, Orland Township, Palatine, Palatine Township, Palos Heights, Palos Hills, Palos Park, Palos Township, Park Forest, Park Ridge, Phoenix, Posen, Prospect Heights, Proviso Township, Rich Township, Richton Park, River Forest, River Forest Township, River Grove, Riverdale, Riverside, Riverside Township, Robbins, Rogers Park Township, Rolling Meadows, Roselle, Rosemont, Sag Bridge, Sauk Village, Schaumburg, Schaumburg Township, Schiller Park, Skokie, South Barrington, South Chicago Heights, South Holland, South Township, Steger, Stickney, Stickney Township, Stone Park, Streamwood, Summit, Sutton, Techny, Thornton, Thornton Township, Tinley Park, University Park, West Township, Westchester, Western Springs, Wheeling, Wheeling Township, Will County, Will County, Illinois, Willow Springs, Wilmette, Winnetka, Woodridge, Worth, Worth Township
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. More than 40% of all residents of Illinois live within Cook County. As of 2020, the population was 5,275,541. Its county seat is Chicago, the most populous city in Illinois and the third-most-populous city in the United States.
Cook County was incorporated in 1831 and named for Daniel Pope Cook, an early Illinois statesman. It achieved its present boundaries in 1839. Within one hundred years, the county recorded explosive population growth going from a trading post village with a little over 600 residents to four million citizens, rivalling Paris by the Great Depression. During the first half of the 20th century it had the absolute majority of Illinois's population.
There are more than 800 local governmental units and nearly 130 municipalities located wholly or partially within Cook County, the largest of which is Chicago. The city is home to approximately 54% of the entire 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. Evanston Township was formerly coterminous with the City of Evanston but was abolished in 2014. County government is overseen by the Cook County Board, and countywide state government offices include the Circuit Court of Cook County, the Cook County State's Attorney, the Cook County Sheriff, and the Cook County Assessor.
Geographically, the county is the sixth-largest in Illinois by land area and the largest by total area. It shares the state's Lake Michigan shoreline with Lake County. Including its lake area, Cook County has a total area of 1,635 square miles (4,234.6 km2), the largest county in Illinois, of which 945 square miles (2,447.5 km2) is land and 690 square miles (1,787.1 km2) (42.16%) is water. Land-use in Cook County is mostly urban and densely populated. Within Cook County, the State of Illinois took advantage of its Lake Michigan access and the Chicago Portage, beginning with the construction of the Illinois and Michigan Canal in 1848. This helped make the region a central transit hub for the nation. Chicago, with its location on the Great Lakes and via the St. Lawrence Seaway, is a global port city, giving Cook County an international shipping port.
Cook County's population is larger than that of 28 different U.S. states and territories, and larger than the population of 11 of the 13 Canadian provinces and territories. Cook County is included in the Chicago metropolitan Combined Statistical Area (CSA), which has a population of approximately 10 million people.