(written from a Production point of view)
Derr was the star of the 1951 science fiction classic When Worlds Collide, co-starring John Hoyt. His other films include Man at Large (1941, with Elisha Cook, Jr.), Castle in the Desert (1942), Joan of Arc (1948, with Jeff Corey), Three in the Attic (1968), The Drowning Pool (1975, with Andrew Robinson and Gail Strickland), American Gigolo (1980), and Firefox (1982, with Ward Costello, Ralph Maurer, and Tony Papenfuss).
Besides TOS, Derr has also appeared on such television series as Perry Mason (one episode with Leslie Parrish, another with Garry Walberg), The Outer Limits, Mannix (including an episode with Jill Ireland and Sabrina Scharf), Starsky and Hutch (starring David Soul), Project U.F.O. (in an episode with Malachi Throne), Taxi (starring Christopher Lloyd), Dallas (with Joanna Cassidy, Susan Howard, Leigh J. McCloskey, William Smithers and Morgan Woodward), and several episodes of Barnaby Jones (starring Lee Meriwether and Vince Howard and also guest-starring the likes of Whit Bissell, Joanne Linville, and Phillip Pine). He also appeared in the 1977 made-for-TV movie SST: Death Flight, along with John de Lancie, Robert Ito, and Brock Peters.
Derr retired from acting in 1983 and went on to become a real estate agent. His final on-screen appearance was an episode of the short-lived Automan, starring fellow TOS guest actor Robert Lansing. Derr died of pancreatic cancer in 1992 at the age of 73.