The islands range in size from over 40 square miles to smaller islands occupied by a single residence, or uninhabited outcroppings of rocks. To count as one of the Thousand Islands, emergent land within the river channel must have at least one square foot of land above water level year-round, and support at least two living trees.
The Thousand Islands archipelago is located at the outlet of Lake Ontario at the head of the Saint Lawrence River. The region is bisected by the Canada-United States border and covers portions of Jefferson and St. Lawrence counties in the U.S. state of New York, in addition to parts of the United Counties of Leeds and Grenville and Frontenac County in the Canadian province of Ontario.
Geologically, the islands are located where a branch of the Canadian Shield runs south across the river to join with the Adirondacks. The Thousand Islands-Frontenac Arch region was designated a World Biosphere Reserve by UNESCO in 2002.
The Thousand Islands Bridge connects New York State and Ontario by traversing Wellesley Island at the northernmost point of Interstate 81 in Jefferson County and meets Highway 137, which leads to Highway 401. The waterfront is served by New York State Routes 12 and 37 and by the Thousand Islands Parkway in Ontario. Ontario also has the Waterfront Trail alongside the Parkway for cyclists who wish to see the area in an alternative way.
Large freighters frequently ply the Saint Lawrence Seaway, but the area has so many shoals and rocks that foreign vessels must use maritime pilots to help them travel through the hazardous waterway. In places, a vessel less than 25 feet (7.6 m) offshore can find itself in over 200 feet (61 m) of water. Conversely, rocks and shoals less than two feet (61 cm) underwater can be found in the center of channels 90 feet (27 m) deep. Due to the great number of rocks and shoals just above or below the water's surface, navigation at night can be dangerous, especially outside of the main channels.
Before the advent of the zebra mussel, visibility of only 10 to 15 feet (3.0 to 4.6 m) was usual, slightly decreasing as the years passed. Water clarity improved markedly in the mid-1990s with the arrival of zebra mussels, which feed on algae. The water is so clear in some areas that a rocky bottom can be observed in 80 feet (24 m) of water. The area has several shipwrecks, and although most of them are over 100 feet (30 m) underwater, some are a mere 15 feet (4.6 m) down and can be seen from the surface.
Prior to European colonization, the Thousand Islands region was home to, or visited by, members of the Iroquois Confederacy and Ojibwa people. Their name for the islands was Manitouana or the "Garden of the Great Spirit".
The region was a part of the War of 1812 between the British Empire and the United States. Many sites from the war can be found, such as Fort Wellington in Prescott, Ontario and the garrison on Chimney Island, Mallorytown, Ontario. Museums about the war can be found on both the Canadian and American side of the river.
In the late 19th and early 20th centuries, many distinguished visitors made the region widely known as a summer resort. During the half century (1874–1912) of the resort's greatest prominence, most wealthy vacationers came from New York City, joined by prominent families from Chicago, Cleveland, Pittsburgh and other cities of the United States and Canada. Several grand hotels provided luxurious accommodations while steamboats offered extensive tours among the islands. Wealthy and middle-class summer residents built summer homes, and the region retains a historically important collection of vacation homes from this time.
Among the lavish homes built during this time were several masonry "castles", some of which remain as international landmarks. The region's first castle, Castle Rest, was built in 1888; it was destroyed in the mid-20th century. The most famous extant examples are "The Towers" on Dark Island, now called Singer Castle, and the previously long-neglected Boldt Castle on Heart Island, which had been left unfinished for over 75 years upon the untimely death of George Boldt's wife. It has since been completed over the recent decades in accord with Boldt's original plans.
The Thousand Islands have long been a center for recreational boating. Large steam yachts, many designed by Nathanael Herreshoff, required distinctive yacht houses. The region was known also for innovative power boating during this period. Three local yacht clubs hosted the Gold Cup Races of the American Power Boat Association for nine consecutive years.
To be considered an island, a piece of land must stay above water throughout the year and support a living tree. Many of the islands are publicly owned. A group of 21 islands form the Thousand Islands National Park, the oldest of Canada's national parks east of the Rocky Mountains. The park hosts campgrounds, inland walking trails, annual family events, as well as a national heritage building.
Thirty New York state parks are managed as part of the New York State Office of Parks, Recreation and Historic Preservation's Thousand Islands Region, including many that are located on river islands or along the New York shore. Many of these river parks were established in the late 19th and early 20th century as part of the St. Lawrence Reservation, and were among New York's earliest land acquisitions for the purpose of preservation and recreational development. Among the larger parks are Wellesley Island State Park, which includes the largest camping complex in the region, and Robert Moses State Park.
Passenger air service to the Thousand Islands region is available in both Ontario and New York. Watertown International Airport (ART) in Watertown, New York has daily service on American Airlines connecting through Philadelphia (PHL). Norman Rogers Airport (YGK) in Kingston, Ontario offers daily service on Air Canada connecting through Toronto Pearson. Both airports also offer private aviation services.
Maxson Airfield (FAA LID: 89NY) is a privately owned, private-use general aviation airport located two nautical miles (3.7 km; 2.3 mi) south of the central business district of Alexandria Bay, a village in Jefferson County, New York. It once had commercial service provided by Mohawk Airlines. At that time, the airport bore the IATA airport code AXB. Maxson is available to the public by Maxson Airfield, LLC.
Brockville-Thousand Islands Regional Tackaberry Airport (IATA: XBR, TC LID: CNL3), also known as Brockville Municipal Airport, is a registered aerodrome located in Elizabethtown-Kitley Township, 4.8 nautical miles (8.9 km; 5.5 mi) northwest of the city of Brockville, Ontario, Canada.
According to The Oxford Companion of Food and Drink, the name for Thousand Island dressing "presumably comes from the Thousand Islands between the United States and Canada in the St. Lawrence River." However, several different versions of the dressing's origin exist. One common story describes how a fishing guide's wife, Sophia LaLonde, made the condiment as part of her husband George's shore dinner. Often in this version, actress May Irwin requested the recipe after enjoying it. Irwin in turn gave it to another Thousand Islands summer resident, George Boldt, who built Boldt Castle between 1900 and 1904. Boldt, as proprietor of the Waldorf-Astoria Hotel, instructed the hotel's maître d'hôtel, Oscar Tschirky, to put the dressing on the menu in 1894.
Sociologists attempting to determine the true origin of Thousand Island dressing found that several conflicting origin stories exist, and that they vary between the various islands and villages of the Thousand Islands region. None appear to have any strong written evidence to support their specific claims.