Sault Ste. Marie is a city in, and the county seat of, Chippewa County in the U.S. state of Michigan. It is on the northeastern end of Michigan's Upper Peninsula, on the Canada–US border, and separated from its twin city of Sault Ste. Marie, Ontario, by the St. Marys River. The city is relatively isolated from other communities in Michigan and is 346 miles from Detroit. The population was 14,144 at the 2010 census, making it the second-most populous city in the Upper Peninsula. By contrast, the Canadian Sault Ste. Marie is much larger, with more than 75,000 residents, based on more extensive industry developed in the 20th century and an economy with closer connections to other communities.

For more than 140 years, the settlement was a single community under French colonial and, later British colonial rule. After the War of 1812, a US–UK Joint Boundary Commission finally fixed the border in 1817 between the Michigan Territory of the USA and the British Province of Upper Canada to follow the river in this area. Whereas traders had formerly moved freely through the whole area, the United States forbade Canadian traders from operating in the United States, which reduced their trade and disrupted the area's economy. The American and Canadian communities of Sault Ste. Marie were each incorporated as independent municipalities toward the end of the nineteenth century.

The city name was derived from the French term for the nearby rapids, which were called Les Saults de Sainte Marie. Sainte Marie (Saint Mary) was the name of the river and Saults referred to the rapids. (The archaic spelling Sault is a relic of the Middle French Period. Latin salta successively became Old French salte (c. 800 – c. 1340), Middle French sault, and Modern French saut, as in the verb sauter, to jump.)

Whereas the modern saut means simply "(a) jump", sault in the 17th century was also applied to cataracts, waterfalls and rapids. This resulted in such place names as Grand Falls / Grand-Sault, and Sault-au-Récollet on the Island of Montreal in Canada; and Sault-Saint-Remy and Sault-Brénaz in France. In contemporary French, the word for "rapids" is rapides.

Sault Sainte-Marie in French means "the Rapids of Saint Mary". The Saint Mary's River runs from Lake Superior to Lake Huron; between what are now the twin border cities on either side.

No hyphens are used in the English spelling, which is otherwise identical to the French, but the pronunciations differ. In French, the name can be written Sault-Sainte-Marie. On both sides of the border, the towns and the general vicinity are called The Sault, or The Soo.

The two cities are joined by the International Bridge, which connects Interstate 75 (I-75) in Sault Ste. Marie, Michigan, and Huron Street in Sault Ste. Marie, Ontario.

Shipping traffic in the Great Lakes system bypasses the rapids via the American Soo Locks, the world's busiest canal in terms of tonnage passing through it. Smaller recreational and tour boats use the Canadian Sault Ste. Marie Canal. The city's downtown was developed on an island, with the locks to the north and the Sault Ste. Marie Power Canal to the south. The largest ships are 1,000 feet (300 m) long by 105 feet (32 m) wide. These are domestic carriers (called lakers). Too large to transit the Welland Canal that bypasses Niagara Falls, they are land-locked. Foreign ships (termed salties) are smaller and can exit the Great Lakes to the St. Lawrence River and the Atlantic Ocean.

For centuries Ojibwe (Chippewa) Native Americans had lived in the area, which they referred to as Baawitigong ("at the cascading rapids"), after the rapids of St. Marys River. French colonists renamed the region Saulteaux ("rapids" in French).

In 1668, French missionaries Claude Dablon and Jacques Marquette founded a Jesuit mission at this site. Sault Ste. Marie developed as the fourth-oldest European city in the United States west of the Appalachian Mountains, and the oldest permanent settlement in contemporary Michigan state. On June 4, 1671, Simon-François Daumont de Saint-Lusson, a colonial agent, was dispatched from Quebec to the distant tribes, proposing a congress of Indian nations at the Falls of St. Mary between Lake Huron and Lake Superior. Trader Nicolas Perrot helped attract the principal chiefs, and representatives of 14 Indigenous nations were invited for the elaborate ceremony. The French officials proclaimed France's appropriation of the immense territory surrounding Lake Superior in the name of King Louis XIV.

In the 18th century, the settlement became an important center of the fur trade, when it was a post for the British-owned North West Company, based in Montreal. The fur trader John Johnston, a Scots-Irish immigrant from Belfast, was considered the first European settler in 1790. He married a high-ranking Ojibwe woman named Ozhaguscodaywayquay, the daughter of a prominent chief, Waubojeeg. She also became known as Susan Johnston. Their marriage was one of many alliances in the northern areas between high-ranking European traders and Ojibwe. The family was prominent among Native Americans, First Nations, and Europeans from both Canada and the United States. They had eight children who learned fluent Ojibwe, English and French. The Johnston’s entertained a variety of trappers, explorers, traders, and government officials, especially during the years before the War of 1812 between Britain and the United States.

As a result of the fur trade, the settlement attracted Ojibwe and Ottawa, Métis, and ethnic Europeans of various nationalities. It was a two-tiered society, with fur traders (who had capital) and their families and upper-class Ojibwe in the upper echelon. In the aftermath of the War of 1812, however, the community's society changed markedly.

The U.S. built Fort Brady near the settlement, introducing new troops and settlers, mostly Anglo-American. The UK and the US settled on a new northern boundary in 1817, dividing the US and Canada along St. Mary's River. The US prohibited British fur traders from operating in the United States. After completion of the Erie Canal in New York State in 1825 (expanded in 1832), the number of settlers migrating to Ohio and Michigan increased dramatically from New York and New England, bringing with them the Yankee culture of the Northern Tier. Their numbers overwhelmed the cosmopolitan culture of the earlier settlers. They practiced more discrimination against Native Americans and Métis.

The falls proved a choke point for shipping between the Great Lakes. Early ships traveling to and from Lake Superior were portaged around the rapids in a lengthy process (much like moving a house) that could take weeks. Later, only the cargoes were unloaded, hauled around the rapids, and then loaded onto other ships waiting below the rapids. The first American lock, the State Lock, was built in 1855; it was instrumental in improving shipping. The lock has been expanded and improved over the years.

In 1900, Northwestern Leather Company opened a tannery in Sault Ste. Marie. The tannery was founded to process leather for the upper parts of shoes, which was finer than that for soles. After the factory closed in 1958, the property was sold to Filborn Limestone, a subsidiary of Algoma Steel Corporation.

In March 1938 during the Great Depression, Sophia Nolte Pullar bequeathed $70,000 for construction of the Pullar Community Building, which opened in 1939. This building held an indoor ice rink composed of artificial ice, then a revolutionary concept. The ice rink is still owned by the city.