James Barnes (December 28, 1806 – February 12, 1869) was a railroad executive and a Union Army general in the American Civil War.

He attended the Boston Latin School and graduated from the United States Military Academy in 1829, ranking fifth out of 46 cadets, in the same class as Robert E. Lee.

However, during Lee's retreat back to Virginia, Barnes saw his first combat when his brigade was attacked by the rearguard of the Confederate Army, resulting in over 200 men shot or drowned in the Potomac River and over 100 more captured.

At the Battle of Fredericksburg in December, Barnes distinguished himself for the first time, leading his brigade in one of the final assaults against Confederate positions on Marye's Heights.

His division commander wrote after the battle, "James Barnes ... is entitled to special notice for his coolness, energy, and marked ability.

[1] In 1863 Barnes' division camped at Union Mills, Maryland, on its way to Pennsylvania, where the Battle of Gettysburg would turn out to be the most significant action in his career.

He was criticized after the battle for withdrawing his two brigades under Colonels Jacob B. Sweitzer and William S. Tilton 300 yards back from the Wheatfield without permission, despite protests from the generals on his flanks.

When reinforcements from the II Corps arrived, Maj. Gen. David B. Birney gave orders for Barnes' men to lie down while the brigade of Brig.