| Frederick Simpson Deitrick | |
| State1: | Massachusetts |
| Term Start1: | March 4, 1913 |
| Term End1: | March 3, 1915 |
| Predecessor1: | Samuel W. McCall |
| Successor1: | Frederick W. Dallinger |
| Office2: | Member of the Massachusetts House of Representatives |
| Term2: | 1902-1905 |
| Predecessor2: | William H. Lewis |
| Birth Date: | 9 April 1875 |
| Birth Place: | New Brighton, Pennsylvania |
| Death Place: | Middleton, Massachusetts |
| Party: | Democratic |
| Alma Mater: | Harvard Law School |
| Occupation: | Lawyer |
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.
Deitrick was elected as a Democrat to the Sixty-third Congress (March 4, 1913 – March 3, 1915) and after an unsuccessful candidacy for reelection in 1914, he resumed practicing law in Boston. He died in Middleton on May 24, 1948, and was interred in Cambridge at Mount Auburn Cemetery.