Martins Ferry is a former settlement in Klamath County and later in Humboldt County, California. It lay on the Klamath River, at an elevation of . It still appeared on maps in 1983.
A post office operated at Martins Ferry from 1861 to 1862 and from 1865 to 1891. There was a military fort at the place in the 1860s. The name honors John F. Martin, its first postmaster, who also operated a ferry.