Cooke was born in Loudoun County on June 13, 1809, and was the son of Stephen Cooke, a physician, and Catherine Esten Cooke. He attended a local school and for two years studied at a Martinsburg academy while living with a much-older brother, John Rogers Cooke (1788–1854), a prominent attorney and member of the Convention of 1829–1830. At age fourteen Cooke entered the United States Military Academy at West Point, New York. On July 1, 1827, he graduated twenty-third in a class of thirty-eight. Commissioned a second lieutenant, he reported to the 6th Infantry Regiment at Jefferson Barracks, in Saint Louis County, Missouri.
After two years of frontier duty beginning in 1828, Cooke was ordered to Cantonment Leavenworth (later Fort Leavenworth), where he met and on October 28, 1830, married Rachel Wilt Hertzog. Their one son and three daughters included, who married J. E. B. Stuart, later a Confederate major general, and who after his death became principal of a Staunton female preparatory school renamed Stuart Hall in her honor.
During the Black Hawk War, Cooke fought at the Battle of Bad Axe in Michigan Territory (later Wisconsin) in August 1832 and became adjutant of the 6th Regiment. Assigned to the new 1st United States Dragoons, he was promoted to first lieutenant on May 10, 1834. (Dragoons were mounted infantry.) Cooke fell ill during a cavalry foray into the unorganized Indian Territory and after he recovered was sent east on a recruiting mission. He was licensed to practice law in Virginia in 1835 and before the Supreme Court of the United States in 1850. Cooke returned to the frontier in 1835 and on July 1 of the next year won promotion to captain. While serving on patrol duty and as regimental drillmaster, he displayed a grasp of tactics that led in 1843 to independent command protecting caravans from marauding Texans and Indians. Cooke gained valuable experience escorting settlers along the Oregon Trail and intervening between warring tribes. Few soldiers had greater knowledge of the frontier inhabitants and trails leading west from Fort Leavenworth.
At the beginning of the Mexican War, Cooke joined the Army of the West and helped accomplish the surrender of Santa Fe in August 1846. Then as a temporary lieutenant colonel he led a battalion of Mormon volunteers on a hazardous three-month trek from Santa Fe to San Diego, California. Promoted to major in the 2nd United States Dragoons on February 17, 1847, Cooke returned to Fort Leavenworth that summer. He was summoned to Washington, D.C., where during the winter of 1847–1848 he was a chief witness against John C. Frémont at a court-martial that convicted the explorer of failing to obey orders in California. Cooke left in March 1848 for Mexico City. From October of that year until October 1852 he served as post commander and superintendent of cavalry recruiting at Carlisle Barracks, in Cumberland County, Pennsylvania. He was brevetted lieutenant colonel in March 1849 in recognition of his service in California.
Cooke reported to Texas late in November 1852 and the following year was ordered to New Mexico Territory, where during the winter of 1853–1854 and the spring he led expeditions against the Jicarilla Apache. He won promotion to lieutenant colonel on February 9, 1854. Cooke helped subdue the Brulé Sioux in the fight at Blue Water Creek in Nebraska Territory on September 3, 1855. As commander of Fort Riley in Kansas Territory in 1855 and 1856, he helped restore order after the bloody clashes between proslavery and free-soil factions. In 1857, as part of an expedition against the Mormons in Utah Territory, Cooke commanded dragoons on a brutal thousand-mile march from Fort Leavenworth to Salt Lake City. He was promoted to colonel on June 17, 1858.
Cooke wrote a memoir, Scenes and Adventures in the Army: or, Romance of Military Life (1857). While on leave of absence in the East in 1858 he began writing a cavalry manual especially for American horse soldiers, based in part on changes in French tactics. As part of his research he traveled to Europe in 1859 to observe Napoléon III’s Italian campaign, which had concluded by the time he arrived. Cavalry Tactics, or Regulations for the Instruction, Formations, and Movements of the Cavalry of the Army and Volunteers of the United States (1861) established Cooke as an authority on the subject and went through several editions.
In August 1860 he took command of the Department of Utah. From his remote posting at Fort Crittenden, Cooke watched the Union fracture. He resisted family entreaties to join the Confederacy. In a letter to the editor of a Washington newspaper written on June 6, 1861, he condemnedand declared, “I owe Virginia little; my country much. She has entrusted me with a distant command; and I shall remain under her flag as long as it waves.”
Secession divided Cooke’s family. One son-in-law commanded a New York regiment in the Union army, but the other two served the Confederacy. Cooke’s son, John Rogers Cooke, resigned his commission in the United States Army and late in 1862 became a Confederate. Of Cooke’s loyalty to the Union J. E. B. Stuart wrote, with mortification, “He will regret it but once & that will be continually.”
Cooke became brigadier general of volunteers in November 1861 and soon thereafter a brigadier in the regular army. He was assigned to the Washington defenses and commanded the reserve cavalry during the(1862). The press and some other officers made Cooke a scapegoat after he failed to check Stuart’s ride around the Union army in mid-June 1862. A controversial cavalry charge at Gaines’s Mill during the near the Confederate capital at further tarnished his reputation, and he left the Army of the Potomac, whose commanders he believed inept. Assigned to courts-martial for about thirteen months, Cooke from October 8, 1863, to April 20, 1864, commanded the District of Baton Rouge. From May 24, 1864, until March 19, 1866, he was posted to New York as superintendent of the regular army’s recruiting service. Cooke was brevetted major general on July 27, 1866, for his wartime service.
Cooke commanded the Department of the Platte from April 1, 1866, until January 9, 1867. His service during the opening months of Red Cloud’s War, fought against a coalition of Plains Indians, was lackluster, and the Fetterman massacre in December 1866 sparked a controversy that led to Cooke’s reassignment to special duty in Louisville, New York, and Philadelphia and then as commander of the Department of the Cumberland for a year beginning on May 1, 1869. He commanded the Department of the Lakes from May 5, 1870, until October 29, 1873, when he retired. Cooke settled in Detroit, Michigan, where he wrote The Conquest of New Mexico and California: An Historical and Personal Narrative (1878) and several magazine articles, including one in Century Magazine in 1885 in which he defended his conduct at Gaines’s Mill. The University of Michigan awarded him an honorary MA in 1883. Late in the 1880s he reconciled with his son, from whom he had been estranged since the beginning of the Civil War. Philip St. George Cooke died at his Detroit home on March 20, 1895, and was buried in Elmwood Cemetery in that city.
- Scenes and Adventures in the Army: or, Romance of Military Life (1857)
- The Conquest of New Mexico and California: An Historical and Personal Narrative (1878)