The opening of the canal at Sault Ste. Marie, in 1855 and the contemporaneous announcement of the railroads' coming had made Duluth the only port with access to the Atlantic and Pacific Oceans. Soon the lumber industry, railroads and mining were all growing so quickly that the influx of workers could hardly keep up with demand and storefronts popped up almost overnight. By 1868 business in Duluth was really booming. "The Zenith City of the Unsalted Seas".

In 1869-1870, Duluth was the fastest growing city in the country and was expected to surpass Chicago in size in only a few years. When Jay Cooke, a wealthy Philadelphia land speculator, convinced the Lake Superior and Mississippi Railroad to create an extension from St. Paul to Duluth, the railroad opened areas due north and west of Lake Superior to iron ore mining. Duluth's population on New Year's Day in 1869 consisted of fourteen families; by the Fourth of July, 3,500 people were present to celebrate. However, Jay Cooke's empire crumbled and the stock market crashed in 1873 and Duluth almost disappeared from the map.

Around the start of the 20th century, the city's port passed New York City and Chicago in gross tonnage handled, elevating it to the leading port in the United States. Ten newspapers, six banks and an eleven-story skyscraper, the Torrey Building, were also present.