Las Vegas, Nevada
Answering that question is difficult. Some obscure gunfighters did not attract the attention of writers. Also, unlike wars, the Old West era does not have a definitive end.
That said, in my opinion, the last gunfighter was John Power, the last surviving member of a shoot-out in the Galiuro Mountains northeast of Tucson, Arizona, on February 10, 1918.
Looking to arrest draft dodgers Tom and John Power, a four-man posse approached the Power cabin about daybreak and opened fire, mortally wounding the boys’ father. The two brothers and pal Tom Sisson returned fire.
The Power brothers and Sisson killed Graham County Sheriff Robert McBride and two deputies. The lone survivor from the posse, Deputy U.S. Marshal Frank Haynes, had approached the cabin from the back when the shooting started, so he did not witness the fight.
Nearly 30 days later, the boys were captured south of the U.S.-Mexico border.
All three were sentenced to life in prison (Arizona had briefly rescinded the death penalty). Sisson died behind bars in 1957. The Power brothers were released in 1960 and pardoned nine years later. Tom died the next year, at age 77, while John died in 1976, at age 84.