Cobb County was one of 10 northwest Georgia counties carved out of Cherokee Indian lands in 1832. Named in honor of former U.S. Senator, Representative and Superior Court Judge Thomas Willis Cobb of Greensboro, the land was first home to Native American settlements including Sweet Water Town on Sweetwater Creek (southwest of Marietta), Big Shanty (later Kennesaw) on Noonday Creek (five miles north of Marietta) and Buffalo Fish (southeast of Marietta).

Marietta, settled in 1833 and designated the county seat in 1834, developed in the geographical center of the new county. Marietta received its official charter in 1852.

Located in the upper Piedmont region, Cobb County had few large plantations, developing instead around small subsistence farms. Towns and settlements grew after the U. S. Army removed the Cherokees to western lands in 1838. By 1850, Marietta was a popular resort community with several hotels attracting summer visitors seeking a cooler, healthier climate than the Georgia and South Carolina coast.

Other towns established in the 1830s were Springville (later Powder Springs, 1838) and Roswell (1839). (The thriving industrial center of Roswell was part of Cobb County until 1932.)

Acworth became a community in the early 1840s and received its city charter in 1860.

Big Shanty, which got its name from the shanty town for railroad construction workers in the late 1830s, received its town charter as Kennesaw in 1887.

Smyrna Camp Ground, which later shortened its name to Smyrna, was a well known religious encampment in the early 1830s and an early railroad stop in the 1840s. Smyrna was incorporated in 1872.

Austell was settled in the late 1800s and chartered in 1885.

During the Civil War (1861-1865), General William T. Sherman led an invading Union army from Chattanooga, Tennessee, toward Atlanta as part of the Atlanta Campaign. Several bloody battles were fought in Cobb in June and July 1864, including the Battle of Kennesaw Mountain.