John B. Allen (May 18, 1845 - January 28, 1903) was an American politician from the state of Washington. He was a Republican.
Allen was born in Crawfordsville, Indiana. He served as a private in the Union Army during the American Civil War. He earned a law degree from the University of Michigan and passed the bar in 1869. He moved to Washington in 1870, and started a law practice in Olympia. He served as United States attorney (1875 - 1885), and as reporter for the supreme court for the Territory of Washington from 1878 to 1885). He was a Republican Delegate to the United States House of Representatives in 1889, and after Washington achieved statehood, he was elected and served in the United States Senate from 1889 to 1893. After the legislature failed to select a Senator for the following term, Allen was appointed by the Governor of Washington, but was not seated by the Senate. After leaving public office, Allen went into private law practice in Seattle.