Glenns Ferry is a city in Elmore County, Idaho, United States. The population was 1,293 at the 2020 census. The city is adjacent to Inter…Glenns Ferry is a city in Elmore County, Idaho, United States. The population was 1,293 at the 2020 census. The city is adjacent to Interstate 84 and the Snake River. Glenns Ferry was one of the most famous and treacherous river crossings on the Oregon Trail. Pioneers forded the Snake River at the Three Island Crossing until 1869, when Gustavus "Gus" Glenn constructed a ferry about two miles upstream, primarily to expedite freight but also for emigrants. His boat, which could hold two wagons, cut nearly twenty miles from the former route. In 1871 the city of Glenns Ferry was established. Construction of the Oregon Short Line Railroad through the town in 1883 gave the city its first major employer.