Juncus castaneus is a species of rush known by the common name chestnut rush. It has a circumboreal or circumpolar distribution, occurring throughout the northern latitudes of the Northern Hemisphere. It occurs in Europe, Asia, and North America. In North America it occurs from Alaska to Greenland, its distribution spanning Canada and extending south through the Rocky Mountains in the contiguous United States. It is widespread and common in the Canadian Arctic Archipelago.