Adin Ballou Underwood (May 19, 1828 – January 24, 1888) was a general in the Union Army during the American Civil War.

In 1862 he joined the new 33rd Massachusetts Infantry Regiment as a Major and served in that unit; eventually becoming its Colonel in April 1863.

[1] After the Gettysburg Campaign the XI Corps, of which the regiment was part of, transferred to the west.

On October 29, at the Battle of Wauhatchie, Underwood was shot in the thigh and crippled for life.

Returning to Boston; he served as surveyor of the port and practiced law again.