Donnelly is a small city in Valley County, Idaho, United States, located in the Long Valley between the West Mountains and the Salmon River Mountains. The community sits in a scenic mountain environment surrounded by forests, open valleys, rivers and numerous lakes, with the rugged landscapes of central Idaho extending in several directions. Its location provides a transition between the agricultural and ranching areas of the Long Valley and the extensive mountain wilderness of the surrounding region.

The area around Donnelly is closely connected with Lake Cascade, a large reservoir on the North Fork of the Payette River. The lake provides opportunities for boating, fishing, swimming and other water-based recreation during the warmer months, while its surrounding forests and mountain views create a popular setting for camping and sightseeing. The Payette River system also contributes to the area's landscape, flowing through valleys and mountain terrain before continuing south toward the Boise region.

Donnelly experiences pronounced seasonal changes, with warm summers and cold, snowy winters. Snowfall is an important part of the local environment and supports winter activities throughout the surrounding mountains. Nearby Tamarack Resort provides skiing and snowboarding during winter as well as mountain recreation during warmer months, while the extensive public lands around Donnelly offer opportunities for hiking, mountain biking, hunting, fishing and wildlife observation.

The community has its roots in the development of central Idaho's timber, ranching and transportation industries. Today, Donnelly retains a small-town character while serving as a gateway to the recreational landscapes of Valley County. The surrounding forests, mountain ranges, waterways and open valleys give the area a distinctly rural and alpine character, with outdoor recreation playing an important role in the local economy and identity.

Donnelly's position between Lake Cascade and the surrounding mountain ranges makes it a convenient base for exploring central Idaho. The combination of high-country scenery, forests, reservoir shoreline and year-round recreation provides a varied landscape that changes considerably with the seasons, from green mountain valleys in summer to snow-covered forests and peaks during winter.