Yukon–Koyukuk Census Area is a census area in the U.S. state of Alaska. As of the 2020 census, the population was 5,343, down from 5,588 in 2010. With an area of 147,842.51 sq mi (382,910.3 km2), it is the largest of any county or county-equivalent in the United States, or slightly larger than the entire state of Montana. It is part of the unorganized borough of Alaska and therefore has no borough seat. Its largest communities are the cities of Galena, in the west, and Fort Yukon, in the northeast.

The Koyukuk River is a 425-mile (684 km) tributary of the Yukon River, in the U.S. state of Alaska. It is the last major tributary entering the Yukon before the larger river empties into the Bering Sea.