Loos was born to John George Loos and the former Katherine Pauley in Friend in Saline County in southeastern [[Nebraska]]. He graduated in 1935 from Harvard High School in Harvard in Clay County near Hastings, Nebraska. In 1939, he received a Bachelor of Arts degree from the University of Nebraska at Lincoln, a member of Phi Beta Kappa and a "Regent Scholar with Distinction." He was also affiliated with the Pi Mu Epsilon, a national mathematics honor fraternity. In 1940, he received his Master of Arts degree from the University of Nebraska, where he was a university fellow. Loos then served for five years in the [[United States Army]] in the South Pacific during [[World War II]]. He was an artillery officer who was promoted to major and a recipient of the [[Bronze Star]] medal for meritorious service.<ref name=obit>{{cite web|url=http://www.legacy.com/obituaries/theadvocate/obituary.aspx?n=john-louis- loos&pid=1538830166|title=John L. Loos|publisher=''Baton Rouge Morning Advocate'', October 1, 2011|accessdate=October 1, 2011}}</ref>
From 1948 to 1951, Loos was an assistant [[professor]] at Evansville College in Evansville, [[Indiana]]. He received his Ph.D. in history from [[Washington University]] in [[St. Louis]], [[Missouri]]. From 1953 to 1955, he was an instructor of United States history at the John Burroughs School in St. Louis.<ref name=obit/>
==Academic career==