George Sigourney Acker (December 25, 1835 – September 6, 1879) was a Union Army officer in the American Civil War.

Early in the conflict, Acker enlisted in the 1st Michigan Cavalry and was commissioned as captain of Company I.

He then participated in the operation against the raids of Confederate General John Hunt Morgan in Kentucky and Ohio.

After the capture of Morgan, Acker was posted with his regiment in the forces of General Ambrose Burnside in eastern Tennessee.

After this campaign, he was assigned to General William Tecumseh Sherman and participated in the march to the sea and the countryside of the Carolinas.