Samuel Peter Heintzelman was born on September 30, 1805, in Manheim, Pennsylvania. He was the son of Peter and Ann Elizabeth Grubb Heintzelman. Heintzelman’s father was a merchant who also served as the village postmaster.
U.S. Military Academy Cadet
Heintzelman entered the United States Military Academy in 1822, graduating in 1826, seventeenth in his class of forty-one cadets. Among his classmates was future Confederate General Albert Sidney Johnston.
U.S. Army Officer
After leaving West Point, officials commissioned Heintzelman as a brevet second lieutenant in the 2nd U.S. Infantry on July 1, 1826. For several years, he served on garrison duty near the Canadian border at Fort Gratiot, Fort Mackinac, and Fort Brady. On March 4, 1833, authorities promoted Heintzelman to first lieutenant. He then served on quartermaster duty in Florida during the Second Seminole War (December 23, 1835-August 14, 1842). On July 7, 1838, he received a promotion to captain.
Heintzelman married Margaret Stewart of Albany, New York, on December 5, 1844, in Buffalo, New York. The marriage produced two children, a daughter named Mary, and a son named Stewart, who also became an officer in the U.S. Army.
During the Mexican-American War (April 25, 1846-February 2, 1848), Heintzelman served with General Winfield Scott‘s army. On October 9, 1847, officials brevetted him to the rank of major for “gallant and meritorious service” in the Battle of Huamantla.
At the conclusion of the Mexican-American War, Heintzelman transferred to California and then to the Arizona Territory. In December 1851, Heintzelman led a campaign against the Yuma Indians. During the campaign, he established Fort Yuma near the confluence of the Colorado River and the Gila River. Officials brevetted Heintzelman to the rank of lieutenant colonel for his leadership during the campaign. On March 3, 1855, Heintzelman received a promotion to major of the 1st U.S. Infantry while campaigning against Indians along the Rio Grande.
During his time in the Southwest, Heintzelman also found employment as president of the Sonora Exploring and Mining Company, serving as director of its field operations for a brief period while on leave from the army.
In 1859, officials transferred Heintzelman to Texas. While serving there, he led a campaign known as the First Cortina War, against Mexican outlaw and folk hero Juan N. Cortina.
Wounded at Frist Bull Run
When the American Civil War began, Heintzelman was serving in New York. Officials promoted him to the rank of colonel on May 14, 1861, and placed him in command of the newly formed 17th U.S. Infantry. Three days later authorities commissioned Heintzelman as a brigadier general in the volunteer army and gave him command of the 3rd Division of the Army of Northeastern Virginia, serving under Brigadier General Irvin McDowell. Heintzelman took part in the Union debacle at the First Battle of Bull Run on July 21, 1861. During the fighting, a gunshot shattered his elbow.
Major General of Volunteers
Following First Battle of Bull Run, U.S. President Abraham Lincoln called upon Major General George B. McClellan to lead the Union war effort. McClellan soon set about reorganizing the Union armies in the field, but Lincoln had his own designs. On March 8, 1862, the President issued War Order No. 2, merging the Army of the Potomac’s divisions into five corps. Lincoln also named Irvin McDowell, Brigadier General Edwin V. Sumner, Brigadier General Erasmus D. Keyes, Major General Nathaniel P. Banks, and Heintzelman to command the five corps. On March 13, 1862, a disgruntled McClellan issued General Orders, No. 101 (Army of the Potomac), confirming the President’s selections. On May 5, 1862, Heintzelman received a promotion to major general of volunteers.
During the Peninsula Campaign Heintzelman took part prominently in the Siege of Yorktown (April 5, 1862-May 4, 1862), the Battle of Williamsburg (May 5, 1862), the Battle of Seven Pines (May 31, 1862-June 1, 1862), the Battle of Savage’s Station (June 29, 1862), the Battle of Glendale (June 30, 1862), and the Battle of Malvern Hill (July 1, 1862). Army officials brevetted Heintzelman to the rank of brigadier-general in the regular army for “gallant and meritorious conduct” at the Battle of Seven Pines.
Second Bull Run
When McClellan’s Peninsula Campaign fell apart, Confederate General Robert E. Lee launched an offensive against Major General John Pope‘s newly formed Army of Virginia near Manassas, Virginia. To counter Lee’s Northern Virginia Campaign, federal officials began shifting troops from McClellan’s army to Pope’s command. Heintzelman’s corps joined Pope’s army in time to take part in the Union disaster at the Second Battle of Bull Run (August 28, 1862-August 30, 1862).
The performance of Heintzelman’s two more-celebrated divisional commanders, Joseph Hooker and Philip Kearny, often overshadowed Heintzelman’s own stature as a corps commander. Still, Civil War historians generally agree that Heintzelman’s lackluster performance during the Peninsula and Northern Virginia Campaigns exposed his shortcomings in leading large numbers of soldiers. The War Department’s decision to remove Heintzelman from combat command a few months later supports that assessment. On February 2, 1863, officials reassigned Heintzelman to command the 22nd Corps, responsible for the defense of Washington, DC. Heintzelman served in that position until October 13, 1863, when authorities reassigned him to command the Northern Department, headquartered in Columbus, Ohio, where he remained until October 1864. Afterward, Heintzelman served on court-martial duty for the rest of the war.
Post-Civil War Career
Heintzelman retired from volunteer service on August 24, 1865, but he remained in the regular army, commanding the 17th U.S. Infantry, mostly in Texas. He retired from the army on February 22, 1869. A special act of Congress, enacted on April 29 of that year, elevated Heintzelman to the rank of major general for “wounds received in the line of duty.”
Death and Burial
Heintzelman spent his remaining years living in Washington, DC., where he died on May 1, 1880, at age seventy-five. He is buried in Forest Lawn Cemetery, Buffalo, New York.