Donnelly is a city in rural Valley County, Idaho, United States. The population was 138 at the 2000 census, and was estimated to be 148 in 2007. Donnelly is in the Long Valley of Valley County, at an elevation of 4865 feet (1429 m) above sea level. It is on the northeast shore of Lake Cascade (Cascade Reservoir), between the two major cities in the county. McCall is 13 miles (21 km) north, and Cascade is 16 miles (26 km) to the south, via Highway 55. The defunct Tamarack Resort (2004–09) is across the reservoir, to the southwest.