1810 - 19 June 1894 - Age 84.
Picture of Ewell Hall at the College of William and Mary. There is also info here about Ewell himself.
Cullum #664. B-DC: A-VA: Arty: Asst Prof USMA 32-36: Resd36: Prof Math several colleges 39-58: Pres William & Mary College 54-58 & 66-68: CO 32VA Inf CSA: Asst AG GEM JE Johnson to 65: Pres Emeritus Coll W&M 88-94: D-VA 19Jun94 a-84: DAB: Ob-AR 88. [From 1990 Register of Graduates]
Arney, Chris, West Point's Scientific 200: Celebration of the Bicentennial. Biographies of 200 of West Point's Most Successful and Influential Mathematicians, Scientists, Engineers, and Technologists, 2002.
The Columbia Encyclopedia, Sixth Edition, 2001 has a short article: http://www.bartleby.com/65/ew/Ewell-Be.html