Donnelly, Idaho is a city in rural Valley County, Idaho, United States. The population was 152 at the 2010 census.
Donnelly is in the Long Valley of Valley County, on the northeast shore of Lake Cascade (Cascade Reservoir), between the two major cities in the county. McCall is 13 miles north, and Cascade is 16 miles to the south, via Highway 55. Tamarack Resort is across the reservoir to the southwest, accessed through Donnelly.
Donnelly is approximately 85 miles north of Boise, accessed via State Highway 55, the Payette River Scenic Byway, a designated national scenic byway. It heads north from Eagle in Ada County to Horseshoe Bend in Boise County, and climbs the whitewater of the Payette River to Cascade and Donnelly. SH-55 continues north to McCall, where it turns west at Payette Lake and continues to New Meadows in Adams County, ending at the junction with US-95.