John Alexander McClernand (May 30, 1812 – September 20, 1900) is an American lawyer and politician, and a Union general in the American Civil War.

He had been a prominent Democratic politician in Illinois and a member of the United States House of Representatives before the war.

McClernand is firmly dedicated to the principles of Jacksonian democracy and had supported the Compromise of 1850.

McClernand is commissioned a brigadier general of volunteers in 1861.

His is a classic case of the politician-in-uniform coming into conflict with career Army officers, graduates of the United States Military Academy.

He serves as a subordinate commander under Ulysses S. Grant in the Western Theater, fighting in the battles of Belmont, Fort Donelson, and Shiloh in 1861–62.]

A close friend and political ally of Abraham Lincoln, McClernand is given permission to recruit a force to conduct an operation against Vicksburg, Mississippi, which will rival the effort of Grant, his department commander.

Grant is able to neutralize McClernand's independent effort after it conducts an expedition to win the Battle of Arkansas Post, and McClernand becomes the senior corps commander in Grant's army for the Vicksburg Campaign in 1863.

During the Siege of Vicksburg, Grant relieves McClernand of his command by citing his intemperate and unauthorized communication with the press, finally putting an end to a rivalry that has caused Grant discomfort since the beginning of the war.

McClernand leaves the Army in 1864 and serves as a judge and a politician in the postbellum era.