The Copperheads were Northern Democrats who opposed the Civil War and wanted a peace settlement with the Confederates.
Republicans started calling them Copperheads, likening them to the poisonous snake. Interestingly, they accepted the label but because the copperhead to them was the likeness of Liberty, which they cut from copper pennies and proudly wore as badges.
Perhaps the most famous Copperhead was Ohio’s Clement L. Vallandigham. Many counties in Ohio and Indiana continued to exist as a kind of solid south in exile for years along the Ohio River.