William P. Jarrett (August 22, 1877 - November 10, 1929) was an American legal officer and politician.
Jarrett was born and grew up in Honolulu, Hawaii, on the island of Oahu, and attended St. Louis College. He was one of the earliest leaders of the Hawaii Democratic Party. Jarrett served as Sheriff of the City & County of Honolulu from 1906 to 1914 and High Sherriff of the Territory of Hawaii from 1914 to 1922. From March 4, 1923 to March 3, 1927, Jarrett served in the United States Congress as a territorial delegate.
He was interred at Diamond Head Memorial Park. A middle school is named for him.