Yukon Island Main Site, Archaeological site in Kenai Peninsula Borough, Alaska.

Yukon Island is a wooded island in outer Kachemak Bay, about 1 mile (1.6 km) wide and 1.3 miles (2.1 km) long, with a rocky shoreline, steep eroding cliffs and a forest of Sitka spruce and hemlock rising to about 500 feet (150 m). Its main archaeological feature is a large shell midden, the Yukon Island Main Site, a National Historic Landmark.

The main shell midden was found in 1924, when eroding deposits exposed ancient human remains. Frederica de Laguna excavated there in the 1930s and built a 1,500-year chronology of use that later research has largely confirmed. The site was designated a National Historic Landmark in 1962 and listed on the National Register in 1966. A 1976 survey recorded five more middens, one 12 feet deep with radiocarbon dates of CE 1100–1300.

The island's name comes from the Yukon River, far to the north, not from any local Dena'ina word. The 1924 discovery of a woman's remains in an eroding shell midden drew Frederica de Laguna, whose 1930s excavations built a 1,500-year chronology of use. The Yukon Island Center opened in 1991 on land cleared in the 1970s.

Yukon Island lies about 9 miles (14 km) south of Homer, and water taxis run there regularly from Homer for kayakers. The island has no permanent population; the Yukon Island Center, opened in 1991, occupies a small cleared portion and hosts groups of 50–60 people with 24 beds. The nearest mainland is about 1.3 km away, with Hesketh Island roughly 650 m southwest and Cohen Island about 900 m northeast.

A 1964 earthquake caused the island to subside by about 2 feet (60 centimeters), setting off coastal erosion that continuously exposes archaeological materials. This erosion has ironically aided research by revealing artifacts and layers that would otherwise remain hidden.