Colonel Frank Bartow from Chatham County (Savannah) died at the First Manassas - First Bull Run and would posthumously be promoted to general. When Cass County decided to change its name because Lewis Cass supported abolition, they chose Bartow as the hero they wished to honor and voted to rename the county on December 6, 1861.
During The Civil War Bartow County was occupied during the Sherman's Atlanta Campaign and was the place where General Sherman began his March to the Sea. While no major battles occurred in the county a number of minor ones did and a major one would have happened if corps commander John Bell Hood had not been concerned about reports coming into his headquarters of Yankees to his rear at Cassville.
After the Atlanta Campaign but before the March to the Sea, Hood again returned to Bartow County, this time as commander of the Army of Georgia. Sherman was effectively using the Western and Atlantic Railroad to supply his troops from the railhead in Chattanooga, Tennessee and fattening his cattle in Bartow County's fields before moving them south to feed his troops. Hood's men, ill-fed and poorly supplied could use the stores in the warehouses so the commander sent Samuel French to fill the pass and deplete the stores near the Allatoona Depot.
In the Battle of Allatoona Pass, the largest battle to occur in Bartow County, French surrounded federal general John Corse in a star fort overlooking the pass but was forced to retreat when he received reports of a significant Union force approaching. This was backed up by a communication from Sherman to Corse intercepted by French that Sherman was "near" although Sherman never left his Kennesaw Mountain stronghold.
To ensure that Georgia did not have the means to rebuild, as Sherman left for Savannah he removed the railroad track from Dalton to Allatoona Pass and destroyed the track south of Allatoona Pass. His last communication with the north occurred in Cartersville on November 12, 1864 and Sherman destroyed Cassville (Bartow County seat at the time) and portions of Kingston and Carterville. As a result the winter of 1864-65 was one of the hardest for Bartow's citizens and saw many citizens leave. In 1867 the county decided to move the county seat to Cartersville.