1810 - 19 June 1894 - Age 84.

• Assistant Professor of Mathematics, USMA, August 31, 1832 to August 31, 1835.
• Assistant Professor of Natural and Experimental Philosophy, USMA, August 31, 1835 to September 30, 1836, the day of his resignation from the Army. 
• Professor of Mathematics, Hampden Sydney College, VA, 1839-1842 and Professor of Mathematics and Natural Philosophy, 1842-1846.
• Professor of Mathematics and Military Science, Washington College, Lexington VA, 1846-1848.
• Professor of Mathematics and Acting President, William and Mary College, VA, 1848-1849.
• Professor of Mathematics and Natural Science, William and Mary College, 1849-1858.
• President of William & Mary College 1854-1858 & 1866-1868; President Emeritus 1888-1894.
   

Picture of Ewell Hall at the College of William and Mary. There is also info here about Ewell himself.

Obituaries:

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]

References:

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