How Sugar Island Became American: The Webster-Ashburton Treaty of 1842

Evolution of Michigan’s Legal Boundaries

August 9, 1842, marked a turning point in Michigan’s map—and the map of the entire U.S.—when the Webster-Ashburton Treaty was signed, settling several long-standing border disputes between the United States and Great Britain. Among the many results of this treaty was the decision that Sugar Island (then known to Canadians as St. George’s Island) in the St. Mary’s River would become part of Michigan and the United States.

At the heart of the treaty were the efforts of U.S. Secretary of State Daniel Webster and British diplomat Lord Ashburton to put an end to growing tensions over unclear borders, especially in the northeast. The Aroostook War—a bloodless boundary dispute between Maine and British-controlled New Brunswick—had made the need for clarity all the more urgent.

The treaty didn’t just settle the Maine-New Brunswick border. It reached deep into the Great Lakes region, defining the international border between Lake Superior and the Lake of the Woods—a process that highlighted just how tricky early mapmaking had been. The original maps used back in the 1783 Treaty of Paris negotiations, including the error-prone Mitchell Map, left gaping ambiguities in the precise line separating the two nations. Those discrepancies even led to disputed ownership of Minnesota’s Arrowhead region for decades.

Deciding on a Border Route

Several potential border routes were on the table, reflecting both British and American interests. The British favored a path starting from modern Duluth, Minnesota, through a series of rivers, while the Americans preferred older fur-trading routes used by French explorers like Jacques de Noyon in the 17th century. The final decision? A route that followed the well-trodden Grand Portage and Pigeon River path—an agreement that brought lasting stability to this section of the border.

For Michigan, the treaty’s biggest takeaway was the clear designation of Sugar Island as part of the United States. Nestled in the St. Mary’s River between Michigan’s Upper Peninsula and Ontario, Sugar Island is a beautiful and serene place today, but in 1842 it symbolized much more: the peaceful negotiation of boundaries and a step toward ending conflict.

The Webster-Ashburton Treaty also tackled other major issues, including extradition agreements for criminals, a shared use of the Great Lakes, and a joint commitment to ending the transatlantic slave trade.

It’s fascinating to think how these quiet diplomatic decisions from nearly two centuries ago continue to shape the maps we use today—and the places we call home. So next time you find yourself near Michigan’s Sugar Island, remember the diplomatic dance that placed it under the stars and stripes on this very day in history.

Did you know that Sugar Island almost became the headquarters of the United Nations? Read all about it by clicking here.

Marisa Fancy along with her husband and four children dreamt of moving “Up North”. They had vacationed for years in northern Michigan and in 1995 they finally made the move.

The family was always out exploring, but with 4 kids there was some limitations on what they could do. Marisa discovered the amazing network of trails in Northern Michigan after Steve died and she would walk for miles. The trails provided her with peace, comfort and solitude at a difficult time in her life. Later, after meeting Guy who would become her second husband, she learned to golf and found another passion she could enjoy in beautiful Northern Michigan.

Marisa has been the family historian, writer, and poet for as long as she can remember. She has always loved to write and has now found a creative outlet for it other than family. You can read her articles in Adventures in Northern Michigan, Northern Michigan History and Golf Up North.