The steamboat that carried smallpox up the Missouri River and killed 17,000 Plains Indians in 1837

The SS St Peters Smallpox Disaster

At Fort Union Trading Post National Historic Site in North Dakota, you can walk through the reconstructed buildings where one of America’s most devastating epidemics began.

The Bourgeois House visitor center displays exhibits about the fur trade era, while the Trade House comes alive with living history programs during summer.

But this remote outpost along the Missouri River holds a darker story. In 1837, the steamboat SS St.

Peters arrived here carrying more than just trade goods and passengers.

It brought smallpox, unleashing a plague that would kill over 17,000 Native Americans and nearly wipe entire tribes from existence.

The epidemic started with poor decisions, spread through celebration, and ended with one of the most tragic chapters in Plains Indian history.

A Deadly Cargo Sailed Upriver in Spring 1837

The American Fur Company boat SS St Peters left St Louis in spring 1837, loaded with trade goods for Missouri River trading posts. No one knew the boat carried something much more dangerous than furs and supplies.

A black deckhand soon showed signs of smallpox, with fever and sores on his skin. Captain Bernard Pratte Jr had to choose: keep sick crew members away from others or stick to his schedule.

He picked money over safety. The sickness quickly spread as the boat moved north toward Fort Leavenworth, Kansas.

Warnings Went Unheeded at Fort Leavenworth

The St Peters stopped at Fort Leavenworth around April 29, 1837. By then, the sick deckhand clearly had smallpox.

Despite this danger, three Arikara women got on the boat to go back to their villages upriver. These women already showed early signs of being sick.

Soldiers and doctors at the fort told Captain Pratte to take sick passengers off the boat and wait. He said no.

Money mattered more than health advice. The boat kept going north with many sick people on board.

Trader Halsey Unknowingly Boarded a Death Ship

At Fort Pierre, South Dakota, fur trader Jacob Halsey and his pregnant wife got on the St Peters. Halsey looked forward to his new job as manager at Fort Union.

He had gotten a smallpox shot earlier in life and thought he was safe. He was wrong.

Both Halsey and his wife caught the disease during their trip upriver. The virus kept spreading among passengers as the boat got closer to Mandan land.

Celebration Turned to Tragedy at Fort Clark

The St Peters stopped at Fort Clark near Mandan villages on June 19, 1837.

Even though people knew about the sickness on board, including the three sick Arikara women, everyone started to party. Traders, workers, and Native Americans mixed freely during the 24-hour stop.

They sang, danced, and traded while the deadly virus passed between them.

Fort Clark boss Francis Chardon heard about the smallpox cases and quickly took his young son off the boat.

The Fort Union Manager Lost His Family

When the St Peters reached Fort Union in late June, Jacob Halsey was in bed with full-blown smallpox. Several crew members had already died during the trip.

Halsey’s family faced tragedy when his pregnant wife gave birth to a daughter and then died from the disease. Fort workers tried to keep Native Americans away from the fort.

Only Halsey showed visible signs of sickness when the boat arrived, giving false hope that they might control the outbreak.

One Man’s Misguided Attempt Spread Death Faster

Charles Larpenteur, a clerk at Fort Union, thought he could help. He scraped pus from Jacob Halsey’s smallpox sores to make a homemade vaccine.

After checking Dr. Thomas’s medical book but lacking proper vaccine material, Larpenteur went ahead with his plan.

He cut the arms of about 30 Native American women living at the fort and rubbed Halsey’s infected pus into their cuts. Instead of helping, this "vaccination" put the full-strength virus directly into their blood.

The Stench of Death Surrounded Fort Union

Within 15 days of Larpenteur’s failed vaccine attempt, Fort Union stank of death. The smell could be noticed 300 yards away.

Many of the "vaccinated" Native women died in pain. Some went crazy from fever while others had bodies partly eaten by maggots before dying.

A man named John Brazo had the daily job of taking bodies to the bushes around the fort. He sometimes carried loads of three or more dead bodies at once.

Mandans Faced Near-Complete Annihilation

The first Mandan death from smallpox happened on July 14, 1837, in a village near Fort Clark. The disease tore through their packed earth houses where big families lived together.

By August 11, Fort Clark trader Francis Chardon wrote in his journal that he couldn’t count the dead because "they die so fast it is impossible.

" The Mandan tribe, which had about 2,000 people in July, dropped to fewer than 30 survivors by October 1837.

The Virus Jumped From Tribe to Tribe

Assiniboine groups kept coming to Fort Union to trade despite warnings about the disease. The fort’s translator couldn’t convince them to stay away.

Even when traders avoided direct contact with Native visitors, the infected air around the fort spread the disease. A boat trip carried smallpox up the Marias River to Fort McKenzie, bringing it to the Blackfeet people.

The Arikara, Hidatsa, and other Missouri River tribes lost many people as the sickness moved west.

Winter Brought No Relief From Suffering

By winter 1837-38, over 17,000 Native Americans along the Missouri River had died from smallpox. Two-thirds of the Blackfeet people perished.

Half the Assiniboine and Arikara tribes died. One-third of the Crow tribe got the disease and died.

Bodies piled up in mass graves or got thrown into rivers, making water supplies dirty. Surviving tribal members became too weak to hunt, gather food, or protect their land from enemies.

Empty Villages Reshaped the American West

The epidemic finally stopped around 1840 after spreading thousands of miles from the Missouri River to Alaska. The Mandan tribe nearly disappeared, with only 23 to 138 survivors from their original 2,000 people.

The huge death toll created open spaces across the Plains.

Lakota Sioux moved into lands emptied by the epidemic, completely changing who controlled the region. The 1837 smallpox epidemic killed more Plains Indians than any other disease outbreak in North American history.

Visiting Fort Union Trading Post

Fort Union Trading Post is where the devastating smallpox epidemic began when the SS St. Peters docked in 1837.

You can visit this historic site for free at 15550 HWY 1804 near the Montana-North Dakota border.

The Bourgeois House visitor center is open daily (except major holidays) from 9am-5:30pm in winter and 8am-8pm in summer. Check out the Trade House with its living history demonstrations when in season.

For a unique perspective, walk the Bodmer Overlook Trail to see where artist Karl Bodmer painted the fort in 1833.

This article was created with AI assistance and human editing.

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