Letha is an unincorporated community in Gem County, Idaho, United States. The community is located 8 mi (13 km) west of Emmett. The Payette River flows northeast of Letha.
Letha was founded by W.W. Wilton and a Colonel Barnard and named for Wilton's daughter, Letha Wilton. It was built approximately midway along the railway running from Emmett to New Plymouth, with anticipation that it would become a major rail center; although this never occurred, Letha today remains a service center for the adjacent farms and ranches. The community includes an elementary school, fire department, post office, general store, and motor vehicle service station. Higher education, police, medical and legal services are found at nearby Emmett.