Question: In which county did the family of the first man who drove cattle from Texas into Montana build a tribute to a fallen family member of the 163rd Infantry Regiment?

Context paragraphs:
3rd Infantry Brigade, 2nd Infantry Division: At the time of its activation, the 2nd Infantry Division was composed of the 3rd Infantry Brigade, which included the 9th Infantry Regiment; the 23rd Infantry Regiment and the 5th Machine Gun Battalion; the 4th Marine Brigade, which consisted of the 5th Marine Regiment, the 6th Marine Regiment and the 6th Machine Gun Battalion; 2nd Brigade of field artillery; and various supporting units.

163rd Ohio Infantry: The 163rd Ohio Volunteer Infantry (or 163rd OVI) was an infantry regiment in the Union Army during the American Civil War.

163rd Infantry Regiment (United States): The 163rd Infantry Regiment is a regiment of the Montana National Guard.

18th Arkansas Infantry Regiment (Marmaduke's): The 18th Arkansas Infantry (Marmaduke's) (1861–1865) was a Confederate Army infantry regiment during the American Civil War.  The unit was also briefly identified as the 1st Arkansas Infantry Battalion.  The unit was most often referred to as the 3rd Confederate Infantry Regiment.  The designation "Confederate Infantry Regiment" was intended to convey the difference between Provisional Confederate Army units and Regular Confederate Army Units, with Provisional units being those regiments who received a state designation such as "XX Arkansas Infantry Regiment".  In practice, the designation was most often utilized when Regiments were assembled utilizing companies from more than one confederate state.  The "3rd Confederate Infantry Regiment" is occasionally misidentified as the 3rd Arkansas Infantry Regiment commanded by Colonel Van H. Manning.

103rd Infantry Regiment (United States): The 103rd Infantry Regiment was an infantry regiment of the United States Army that served in combat in the American Civil War, World War I, and World War II.  It was an Army National Guard regiment from the states making up New England, but most of its soldiers came from Maine.  It was a part of the 26th Infantry Division and the 43rd Infantry Division.  The 103rd regiment fought in numerous battles before its deactivation after the Second World War.

Nelson Story: Nelson Story, Sr. (April 4, 1838 – March 10, 1926) was a pioneer Montana entrepreneur, cattle rancher, miner and vigilante, who was a notable resident of Bozeman, Montana.  He was best known for his 1866 cattle drive from Texas with approximately 1000 head of Texas Longhorns to Montana along the Bozeman Trail—the first major cattle drive from Texas into Montana.  His business ventures in Bozeman were so successful that he became the town's first millionaire.  In 1893, he played a prominent role in the establishment of the Agricultural College of the State of Montana by donating land and facilities.  He built the first "Story Mansion" on Main Street in Bozeman in 1880 and later built today's Story Mansion at the corner of Willson and College for his son, T. Byron Story in 1910.  In his later years, he became a prominent real estate developer in Los Angeles, California.

17th Infantry Regiment (United States): The 17th Infantry Regiment is a United States Army infantry regiment.  An earlier regiment designated the 17th Infantry Regiment was organized on 11 January 1812, but it was consolidated with four other regiments as the 3rd Infantry in the post-war reorganization of the army following the War of 1812, due to the shattering losses it sustained at the River Raisin.  The current 17th Infantry was constituted as the 17th Regiment of Infantry on 3 May 1861.

Soldiers Chapel: Soldiers Chapel is a non-denominational Christian memorial chapel in Big Sky, Gallatin County, Montana, USA, dedicated in 1955 by the Nelson Story family in tribute to a fallen family member of the 163rd Infantry Regiment.  The regiment was part of the Montana National Guard during World War II.  Open daily from Memorial Day through Labor Day, with services at 11 a.m. on Sundays, the chapel is popular for special events such as weddings.  The chapel is at an elevation of 6017 ft .

153rd Infantry Regiment (United States): The 153d Infantry Regiment (First Arkansas) is a United States infantry regiment, currently represented in the Arkansas Army National Guard by the 1st Battalion, 153rd Infantry, headquartered at Malvern, Arkansas, and 2nd Battalion, 153rd Infantry, headquartered at Searcy, Arkansas, elements of the 39th Brigade Combat Team.  The regiment was also represented by the 3rd Battalion, 153rd Infantry Regiment headquartered at Warren, Arkansas until that unit was deactivated on 5 September 2005.  The regiment was activated as the 1st Arkansas Volunteer Infantry for the Spanish-American War, but did not deploy overseas.  The regiment was activated for World War I, redesignated as the 153rd Infantry and shipped to France as a part of the 39th Division, but became a replacement division and personnel were reassigned to other AEF units.  The regiment was activated for World War II and deployed to the Aleutian Islands, participating in the Aleutian Islands Campaign.  Recently, elements of the regiment have participated in two deployments in support of Operation Iraqi Freedom, in 2004 and again in 2008.

503rd Infantry Regiment (United States): The 503rd Infantry Regiment, formerly the 503rd Parachute Infantry Regiment (PIR) and the 503rd Airborne Infantry Regiment (AIR), is an airborne infantry regiment of the United States Army.  The regiment served as an independent regiment in the Pacific War during World War II; at Fort Campbell, Kentucky; in Okinawa, Japan; and in Germany.  Regimental elements have been assigned to the 2nd Infantry Division, the 11th Airborne Division, the 24th Infantry Division, the 82nd Airborne Division, and the 173rd Airborne Brigade Combat Team.  Regimental elements have participated in campaigns in the Vietnam War, Operation Enduring Freedom–Afghanistan, and Operation Iraqi Freedom.  The regiment claims 15 Medal of Honor recipients: two from World War II, 10 from Vietnam, and three from Afghanistan.  A parent regiment under the U.S. Army Regimental System.  The regiment's 1st and 2nd Battalions are active, assigned to the 173rd Airborne Brigade, based at Caserma Ederle, Vicenza, Italy.

Supporting paragraphs: Soldiers Chapel Nelson Story
Answer: Gallatin County