The town is named for long Long Lake beside which it sits. The town is entirely within the Adirondack Park and is the most northerly town in the county. It is a summer tourism destination offering fishing, hiking, boating, and many other outdoor activities. In the winter months, snowmobiling is also popular. Long Lake is also the home of the historic Adirondack Hotel and Helms Aero Service, floatplane service.
The town was first settled around 1833.
The Town of Long Lake was formed in 1837 from sections of the Towns of Arietta, Morehouse, Lake Pleasant, and Wells. In 1861, the town was increased by additions from Arietta, Lake Pleasant, and Morehouse.
Long Lake is part of the 1.1 million acres (4,500 km²) acquired from the Mohawk Indians as part of the 1771 Totten and Crossfield Purchase. Long Lake is a glacial widening of the Raquette River and is part of the water route that connects the Fulton Chain Lakes with the Saint Lawrence River drainage. This route was frequently traveled by guideboat in the mid-late 19th century. At that time, "a typical trip might start at the Saranacs from which a party could make its way to the Raquette River via Indian Carry and Stoney Creek." The trip continued "via the lakes accessible from it— Long, Raquette, Forked, Blue and Tupper."  Settled by the 1830s, Long Lake was isolated, except by water, until William Seward Webb's Mohawk and Malone Railway was built through what was then known as Long Lake West in 1892. Long Lake and Long Lake West were connected by a stage route. The Mohawk & Malone Railway was taken over by the New York Central Railroad a few years after construction was completed. The town of Long Lake West was later renamed Sabbatis.
Long Lake West was the site of a fire that destroyed most of the town in 1908.
Long Lake is the starting point of the Roosevelt-Marcy Trail. On September 14, 1901 Theodore Roosevelt was climbing Mount Marcy when he got word that President William McKinley, who had been shot two weeks before in Buffalo, New York, but expected to improve, had taken a serious turn for the worse.
Roosevelt rushed down ten miles (16 km) from his campsite at Lake Tear of the Clouds to the closest town and telephone which was outside of Newcomb, New York, approximately away from Long Lake. From there he took a legendary midnight stagecoach ride to the closest train station away at North Creek, New York, where he found out that McKinley had died. Roosevelt was sworn in at Buffalo.