Cobb County was created from Cherokee County, originally part of the Cherokee Indian Nation. It was the 81st county in Georgia and named for Judge Thomas Willis Cobb of Virginia, who served as a U.S. Senator, state congressman and Superior Court Judge.

Marietta was named for Judge Cobb's wife. The city's downtown was destroyed by Sherman's troops in 1864, but it was reconstructed and now Marietta is home to four National Historic Districts listed on the National Register of Historic Places.