John Irvin Gregg

John Irvin Gregg (July 19, 1826 – January 6, 1892) was a career U.S. Army officer. He fought in the Mexican-American War and during the American Civil War as a general officer in the Union army.

Early life and career
John Irvin Gregg was born in Bellefonte, Pennsylvania, the grandson of Andrew Gregg (a U.S. Senator from Pennsylvania) and a cousin of future Union general David McMurtrie Gregg. He was also related to Pennsylvania governor Andrew Gregg Curtin. Gregg served in the "Centre Guards," a Centre County militia unit, as a lieutenant.

During the Mexican-American War, he enlisted as a private in the 2nd Pennsylvania Infantry on December 29, 1846, and was mustered out of the volunteer service on May 6, 1847. He then received promotions to first lieutenant as of February 18, and to captain as of September 5, both in the 11th U.S. Infantry, serving as a recruiting officer. He was honorably discharged on August 14, 1848.

He then entered the iron industry with the firm Irvin, Gregg & Co., owned by family members. He married Harriet Marr, the daughter of a local Presbyterian minister and schoolteacher. They had two sons, Irvin and Robert.

Civil War service
When the Civil War broke out, Gregg was commissioned a captain in the 3rd U.S. Cavalry on May 14, 1861. He then joined the volunteer army in June as a captain in the 34th Pennsylvania Infantry. He resigned soon afterward to accept a commission in the regular army as a captain in the 6th U.S. Cavalry. On November 14, 1862, Gregg was promoted to colonel of the 16th Pennsylvania Cavalry. He then commanded many different cavalry brigades in the various reorganizations of the Army of the Potomac. He led the Third Brigade at the battles of Chancellorsville and Gettysburg in a division commanded by his cousin David Gregg.

In October 1863, he earned another brevet to lieutenant colonel in the regular army for the Battle of Sulphur Springs. He was wounded at the Second Battle of Deep Bottom and won a brevet again on October 7, 1864 to full colonel in the regular army. He was promoted to brevet brigadier general of volunteers on August 1, 1864, for gallant and meritorious service in the engagement and defenses of Richmond on the Brock Turnpike and at the Battle of Trevilian Station.

On April 7, 1865, Gregg was slightly wounded at the Battle of Sayler's Creek, captured the next day north of Farmville, Virginia, and was released two days later. Near the close of the war, Gregg was appointed a brevet major general in the volunteers and brevetted to brigadier general in the regular army, both effective March 13. He briefly was in command of the Cavalry Corps, Army of the Potomac from February 10 to February 24. Gregg was mustered out of the volunteer service on August 11.

Postbellum
After the end of hostilities Gregg remained in the Army. He was named colonel of the 8th U.S. Cavalry on July 28, 1866, a position his cousin David McMurtrie Gregg had desired. He then reported for duty at Camp Whipple in the Arizona Territory. He led a series of expeditions against Indians into the Mojave Desert. He was sent to the New Mexico Territory, where he commanded Fort Union from 1870 to 1872, and led efforts in that region to pursue and subdue the Apache. In 1872, he led a reconnaissance expedition to survey and map the Texas Panhandle.

Gregg retired from active service on April 2, 1879. He died in Washington, D.C., and is buried in Arlington National Cemetery in Virginia.