John Alexander Johnston (22 February 1858 – 5 January 1940) was an American military officer and commissioner of the District of Columbia born in Allegheny, Pennsylvania.

He served as a brigadier general during World War I. Johnston was born in Allegheny, Pennsylvania on February 22, 1858, the son of Alexander and Sarah R.

In 1883, he was an honor graduate from the Infantry and Cavalry School at Fort Leavenworth, Kansas, after which he became an instructor there, instructing on the art of war and engineering until 1885.

[2] Between his tours of frontier duty in South Dakota, Johnston taught history, law and tactics at the U.S. Military Academy from 1887 to 1891, and horsemanship at the Jefferson Barracks Cavalry Depot, Missouri, from 1893 to 1895.

[6]Returning to the United States, Johnston commanded the 153rd Depot Brigade at Camp Dix, New Jersey from January to February 1919, when he was relieved of active duty.