In Glacier National Park, pets on a leash no longer than 6 feet are allowed in developed areas such as: in your cars while driving park roads, frontcountry campgrounds, picnic areas, along roads when you are stopped, in parking areas, and in boats on lakes where motorized watercraft are permitted. Pets are not permitted on trails, along lake shores outside of developed locations, in the backcountry, or in any building.
More information on the Glacier National Park pet policy
