Oscar A. Trippet (March 6, 1856 – July 15, 1923) was a United States federal judge.
Born in Princeton, Indiana, Trippet attended the University of Virginia School of Law. He was in private practice in Princeton, Indiana from 1879 to 1887, then in San Diego, California until 1901, and then in Los Angeles, California until 1915. He was a member of the Indiana State Senate in 1886.
On March 2, 1915, Trippet was nominated by President Woodrow Wilson to a seat on the United States District Court for the Southern District of Californiavacated by Olin Wellborn. Trippet was confirmed by the United States Senate on March 3, 1915, and received his commission the same day. Trippet served in that capacity until his death, in 1923.