Official accounts indicate that Philip Henry Sheridan was born on March 6, 1831, in Albany, New York. His parents immigrated from County Caven, Ireland. When Philip was a very young child they moved to Somerset, Ohio, 43 miles southeast of Columbus. Other accounts indicate that he may have been born at sea while his parents were immigrating from Ireland. The exact date of his birth is also in question. His parents' names were John and Mary Meegham Sheridan. Philip was the third of six children. John Sheridan worked as a sub-contractor building roads and digging canals. Philip grew up in Somerset, attended school there, and clerked in several different stores in town. While still a youngster he demonstrated that he could and would fight. When he fought he usually bested his opponent. While still a child he made it known that someday he intended to join the army.
While working as bookeeper at the local dry goods store in Somerset he became acquainted with U.S. Representative Thomas Ritchey and sought his assistance in getting an appointment to the West Point Military Academy. In March 1848, he was selected and in June he arrived at the Academy. His educational background was weak, but he studied hard and managed to do well enough to progress to his third year when he got into a fight that almost ended his military career before it began. Cadet sergeant William R. Terrill said something that angered Sheridan so he hit him. Terrill was bigger and was on his way to thrashing Sheridan when the fight was broken up. Colonel Henry L. Brewerton, the Military Academy Superintendent, decided that Sheridan was in the wrong and suspended him for one year. Sheridan returned to Somerset to wait out his suspension, but then returned to graduate in the bottom half of his class. Colonel Robert E. Lee, then Superintendent of the Academy, presided over his graduation ceremonies.
In the winter of 1854, Brevet Second Lieutenant Sheridan was assigned to Company D, 1st Infantry Regiment, in Fort Duncan, Texas. (The Secretary of War at the time was Jefferson Davis.) One of Sheridan's first assignments was to patrol the area in search of hostile Comanche and Lipan Apache Indians. He was promoted to second lieutenant in November 1854 and transfered to Company D, Fourth Infantry Regiment at Fort Reading, California. The Pacific Division Commander at the time was John E, Wool. Sheridan arrived in California in July 1855 and was soon assigned to accompany a survey party, led by Lieutenant Robert S. Williamson, that was laying out a possible railroad route from the Sacramento Valley north into Oregon's Willamette Valley. During this expedition, Sheridan commanded a small unit of dragoons. He had several brushes with Yakima Indians before encamping at Fort Dalles on the Columbia River. In the fall of 1855, he was part of Major Gabriel J. Rains's campaign against the Yakima Indians in which he demonstrated personal bravery and qualities of leadership. On March 26, 1856, he was part of the force that successfully responded to an attack by one hundred Yakima and allied Indians on settlements at the Lower and Middle Columbia River Cascades. General-in-Chief Winfield Scott commended Sheridan for "gallant conduct" in the relief of the Cascades settlements.
Sheridan was next sent to the Grande Ronde Indian Reservation near present day Portland, Oregon. After completing the construction of fortifications at nearby Fort Yamhill, he went on to several other posts in the Northwest at which he dealt effectively with an assortment of reservation problems. Again General Scott commended him - this time for possessing a "calm temper." At this time Sheridan took the daughter of a Klikitat Indian Chief as a female companion. Her Klikitat name was Sidnayoh and her English name was Frances. Frances lived with Sheridan for the next several years while he was working effectively with reservation indians in the Northwest (including the troublesome Rogue River Indians) and serving as company quatermaster at Fort Yamhill. With the outbreak of war between the states in 1861, a large number of regular army officers resigned their commissions to join the Confederate Army. In March 1861, Sheridan was promoted to first lieutenant in the wave of promotions that was designed by Washington to replace the officer cadre that had been lost to the Confederacy. In May he was promoted to captain. For a brief period he served as acting commander of Fort Yamhill, but in September 1861, he was ordered to report to Jefferson Barracks, near St. Louis, Missouri.