The peninsula extends approximately 150 miles (240 km) southwest from the Chugach Mountains, south of Anchorage. It is separated from the mainland on the west by Cook Inlet and on the east by Prince William Sound. Most of the peninsula is part of the Kenai Peninsula Borough. Gerasim Izmailov was the first European man to explore and map the peninsula in 1789, though Athabaskan and Alutiiq Native groups have lived on the peninsula for thousands of years.
The glacier-covered Kenai Mountains (7,000 ft/2,130 m) run along the southeast spine of the peninsula along the coast of the Gulf of Alaska. Much of the range is within Kenai Fjords National Park. The northwest coast along the Cook Inlet is flatter and marshy, dotted with numerous small lakes. Several larger lakes extend through the interior of the peninsula, including Skilak Lake and Tustumena Lake. Rivers include the Kenai River, famous for its salmon population, as well as the Russian River, the Kasilof River, and the Anchor River. Kachemak Bay, a small inlet off the larger Cook Inlet, extends into the peninsula’s southwest end, much of which is part of Kachemak Bay State Park