Quincy Adams Gillmore (February 28, 1825 – April 7, 1888) was an American civil engineer, author, and a general in the Union Army during the American Civil War. He was noted for his actions in the Union victory at Fort Pulaski, where his modern rifled artillery readily pounded the fort's exterior stone walls, an action that essentially rendered stone fortifications obsolete. He earned an international reputation as an organizer of siege operations and helped revolutionize the use of naval gunnery.

Gillmore was born and raised in Black River (now the City of Lorain) in Lorain County, Ohio. He was named after the president-elect at the time of his birth, John Quincy Adams.

Gillmore entered the United States Military Academy at West Point, New York, in 1845. He graduated in 1849, first in a class of 43 members. Gillmore was appointed to the engineers and was promoted to first lieutenant in 1856. From 1849 until 1852, he was engaged in constructing the fortifications at Hampton Roads in coastal Virginia. For the next four years, Gillmore was instructor of Practical Military Engineering at West Point and designed a new riding school. He was conferred an honorary A.M. degree by Oberlin College in 1856.

Beginning in 1856, Gillmore served as a purchasing agent for the Army in New York City. He was promoted to captain on August 6, 1861.

With the outbreak of the Civil War in early 1861, Gillmore was assigned to the staff of Brigadier General Thomas W. Sherman and accompanied him to Port Royal, South Carolina. After being appointed as a brigadier general, Gillmore took charge of the siege operations against Fort Pulaski. A staunch advocate of the relatively new naval rifled guns, he was the first officer to effectively use them to knock out an enemy stone fortification. More than 5,000 artillery shells fell on Pulaski from a range of 1,700 yards during the short siege, which resulted in the fort's surrender after its walls were breached.

The result of the efforts to breach a fort of such strength and at such a distance confers high honor on the engineering skill and self-reliant capacity of General Gilmore. Failure in an attempt made in opposition to the opinion of the ablest engineers in the army would have destroyed him. Success, which in this case is wholly attributable to his talent, energy, and independence, deserves a corresponding reward. — New York Tribune

Although he was one of the best artillerists and engineers in the army he was not well respected by his men.

After an assignment in New York City, Gillmore traveled to Lexington, Kentucky, where he supervised the construction of Fort Clay on a hilltop commanding the city. Gillmore commanded a division in the Army of Kentucky then the District of Central Kentucky. Though long associated with engineering and artillery, Gillmore's first independent command came at the head of a cavalry expedition against Confederate General John Pegram. Gillmore defeated the Confederates at the battle of Somerset for which he was given a brevet (military) promotion to colonel in the U.S. Army.