Because HOW I got this information might be as useful as the information itself (the "teach a person how to fish" viewpoint), I'll describe exactly the process I went through, which took about 2 or 3 minutes (helps to have the websites I mention bookmarked).
I began with a search at the Zentralblatt Math search page (because it's freely available, unlike Math. Reviews) and found these 3 papers by him. Then I went to the Mathematics Genealogy Project webpages, where I found that he got his Ph.D. in 1936 under Eric Temple Bell at Caltech. The Math. Genealogy site doesn't give his middle name, so I then went to the ProQuest Search page and entered "Webb, Donald" (quotes included) in the author window and "logics" (quotes not included) in the title window, but I didn't learn anything new. FYI, the ProQuest page is a good place to try if the Math. Genealogy site doesn't give you a middle name. Then I tried a basic google books search, using "Webb, Donald L" + math, where under the short google-excerpts in the "Who's Who in Philosophy" items I learned that he was born on 17 November 1907 in Wakita, Oklahoma; and he got his BS and MS degrees at University of Arizona in 1931 and 1933. Knowing his birth year allowed me to refine the google-books search to "Webb, Donald" + math + 1907, where I intentionally left off his middle initial so that I could possibly determine his middle name, and I was able to see among the excerpts of the hits that his middle name is Loomis (in the "Who's Who in American Education" item). Finally, knowing his middle name, I did a basic google search for "Donald Loomis Webb" (not using "1907", but prepared to include "1907" if there seemed to be more than one person with that name or too many hits to be useful), and I found this gravesite page, where I learned that he died on 1 June 1971 in Tucson, Arizona.
Knowing these details about his life, you should now be able to conduct a variety of searches to find out more about him.