It is named for Daniel Pope Cook, an Illinois Attorney General. The seat and largest city are both Chicago, the third largest city in the United States.
The area is also known for its densely populated urban setting, containing several of the largest cities in Illinois.
It borders Lake, Will, DuPage, Kane and McHenry Counties in Illinois, Lake County in Indiana and Berrien County in Michigan (Across Lake Michigan)
Core Highways include I-55, I-57, I-80, I-88, I-90, I-94, US-14, US-30 and US-41; among many others.