Frederick Simpson Deitrick (April 9, 1875 – May 24, 1948) was a U.S. Representative from Massachusetts. Born in New Brighton, Pennsylvania, Deitrick attended the public schools. He graduated from Geneva College, Beaver Falls, Pennsylvania, in 1895 and from Harvard Law School in 1898. After being admitted to the bar in 1899, Deitrick commenced practice in Boston. He served as a member of the Massachusetts House of Representatives from 1902 to 1905 and as member of the board of aldermen of Cambridge in 1908 and 1909.