Adamson Tannehill (May 23, 1750 – December 23, 1820) was an American military officer, politician, civic leader, and active participant in the early development of Pittsburgh and western Pennsylvania. Born in Frederick County, Maryland, Tannehill was among the first volunteers to join the newly established Continental Army during the American Revolutionary War, serving from June 1775 until 1781. He reached the rank of captain and was commander of the Maryland and Virginia Rifle Regiment, the longest-serving Continental rifle unit of the war. He participated in several major engagements, including the battles of Trenton, Princeton, and Saratoga. After the conflict, Tannehill settled in Pittsburgh, Pennsylvania, his last military posting of the war. He was active in the Pennsylvania state militia, advancing to major general in 1811. Tannehill also served as a brigadier general of United States Volunteers in the War of 1812.

Tannehill was an early citizen of Pittsburgh and a Pennsylvania politician who held local, state, and national appointed and elected offices. These included one session as a Democratic-Republican in the Pennsylvania House of Representatives in 1791, one term in the U.S. House of Representatives from 1813 to 1815, and president of the Pittsburgh branch of the Bank of the United States from 1817 until his death in 1820. He also served on commissions of civic and state organizations. In late 1800, Tannehill, while a justice of the peace, was alleged to have charged more than was allowed by law for two probate cases and was convicted of extortion. Shortly after, the governor of Pennsylvania remitted the charges and reinstated him to office.

Tannehill died in 1820 near Pittsburgh, Pennsylvania. He was buried at his Grove Hill home outside Pittsburgh and reinterred in Allegheny Cemetery in 1849.

Adamson Tannehill was born May 23, 1750, in Frederick County, Maryland, the oldest of nine children born to John Tannehill, owner of a tobacco plantation, and Rachel Adamson Tannehill. Adamson's maternal grandfather took a special interest in the grandchild who bore his name, and he provided "such pecuniary assistance as to secure a fine education" for him. Little else is known of Adamson's youth and upbringing. No portraits of him are known to exist; family records state that as an adult he "was six feet in height, well proportioned and of commanding appearance".

Tannehill was among the first volunteers to enlist in one of the earliest American military units to form when the American Revolutionary War started in the spring of 1775. He served in the Continental Army, initially as the orderly sergeant in Captain Thomas Price's Independent Rifle Company, one of the original 10 independent rifle companies authorized by the Continental Congress on June 14, 1775. He received his officer's commission as a third lieutenant in January 1776 while serving at the siege of Boston. At New York in mid-July, Tannehill and his company were incorporated into the newly organized Maryland and Virginia Rifle Regiment, when he advanced to second lieutenant. That summer and fall, many of the regiment's officers, including Tannehill, recruited for the unit back in the two states and then moved the enlistees to the American army in New York.

In mid-November 1776, a large portion of Tannehill's regiment was captured or killed at the Battle of Fort Washington on northern Manhattan Island. The remainder—about one-third of the unit, including Tannehill, who had still been away recruiting—continued to serve actively in the Continental Army. That winter, they participated in the American victories at the battles of Trenton, Assunpink Creek, and Princeton and in the early 1777 skirmishing in northern New Jersey, a period termed the Forage War. The following spring, they were administratively attached to the 11th Virginia Regiment in part because of the losses suffered by their rifle regiment. The riflemen also served as an experienced, if small, force to bolster this newly formed Virginia unit.

Tannehill was promoted to first lieutenant in May 1777, and the following month he was attached to the just-organized Provisional Rifle Corps commanded by Colonel Daniel Morgan. Deployed as specialized light infantry, this regiment-size force of about 500 riflemen played pivotal roles in the American victories at the battles of Saratoga and White Marsh in late 1777 and a peripheral role in the tactically inconclusive Battle of Monmouth in June 1778. The rifle corps was also notable for its scouting and outpost duties in defense of the Continental Army's Valley Forge encampment during the winter and spring of 1777–1778. For the last half of 1778, Tannehill and the unit served in south-central New York, where they assisted in countering depredations to settlements by Loyalist units and British-allied Iroquois warriors. The most noteworthy operation in which the riflemen participated was the raid on Unadilla and Onaquaga in early October. Tannehill was detached from the rifle corps at the start of 1779, when he returned to the Maryland and Virginia Rifle Regiment (his permanent unit).

In January 1779, Tannehill was ordered to Fort Cumberland, western Maryland, to help recruit three companies "to the full complement" for the undermanned Maryland and Virginia Rifle Regiment. This action was part of a formal reorganization of the unit conducted in advance of the regiment′s relocation to Fort Pitt in western Pennsylvania. Acting under the same orders, Lieutenant Colonel Moses Rawlings, the rifle regiment's commander, was also working that winter and spring to rebuild the unit by recruiting new members and marshaling returning prisoners of war while stationed at Fort Frederick, Maryland. (Rawlings had been captured at the Battle of Fort Washington and exchanged from British captivity in early 1778. After his release, he was assigned command of the prisoner-of-war camp and its militia guard at Fort Frederick. As a result, the elements of the rifle regiment still in the field continued to be led by the company officers.) In furtherance of the officers' efforts to muster their regiment, General George Washington ordered in February 1779 "all the men belonging to [...] Rawlings's Regimt. now doing duty in the line are to be delivered up to Lieutenant Tanneyhill [sic] of said regiment upon his demanding them." Tannehill supervised the assembly of the regiment because of the temporary absence of its acting commander.