Cook County was created on January 15, 1831 by an act of the Illinois State Legislature as the 54th county established in Illinois. The unincorporated Fort Dearborn settlement at the mouth of the Chicago River became the new county's seat. On May 7, 1831, Cook County elected its first officials.
Cook County is an urban county in the upper northeastern section of the State of Illinois that contains more than 800 local governmental units within its boundaries. With a population of approximately 5.3 million people, it is the second most populous county in the nation and the 19th largest government in the United States (2005 census statistics).
It is a home rule county pursuant to Article VII, Section 6 of the Illinois State Constitution and is governed by a 17-member Board of Commissioners who are elected from single-member districts. The Commissioners and a County Board President are elected to four-year terms by the citizens of the County.
Cook County contains 128 municipalities in its region, the most well known being the City of Chicago - which is the County seat where the central offices of Cook County are located. The City of Chicago and the suburban municipalities account for approximately 85% of the County's 946 square miles, while unincorporated areas make up the remaining 15%. The unincorporated areas of the County are under the jurisdiction of the Cook County Board of Commissioners.
As mandated by State law, County government has principal responsibility for the protection of persons and property, the provision for public health services and the maintenance of County highways.