Robert Cowdin (September 18, 1805 – July 9, 1874) was a businessman, a field officer in the Union Army during the American Civil War and a local politician in Massachusetts.

He was appointed brigadier general of volunteers September 26, 1862 and he then commanded a brigade in the defenses of Washington until March 1863.

He did not become a full brigadier general because his appointment expired by law March 4, 1862 when the U.S. Senate adjourned without confirming it.

He also served on the Common Council of Boston for eight years, and various elected positions in the city's correctional system.

[2] On September 26, 1862, based on a recommendation by General Joseph Hooker, he was appointed Brigadier General of Volunteers, and commanded the 1st Brigade, Abercrombie's Division, Defenses of Washington (later called the XXII Corps), from October 1862 to February 1863, then the 2nd Brigade until the end of March.