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 was graduated from Geneva College, Beaver Falls, Pennsylvania, in 1895 and from Harvard Law School in 1898. He was admitted to the bar in 1899 and commenced practice in Boston, Massachusetts. He served as member of the board of aldermen of Cambridge in 1908 and 1909. He served as member of the Massachusetts House of Representatives, 1902-1905.
Deitrick was elected as a Democrat to the Sixty-third Congress (March 4, 1913-March 3, 1915). He was an unsuccessful candidate for reelection in 1914 to the Sixty-fourth Congress. He resumed the practice of law in Boston, Massachusetts. He died in Middleton, Massachusetts, May 24, 1948. He was interred in Mount Auburn Cemetery, Cambridge, Massachusetts.