Fort Sarpy

Friday, August 28, 2026

Fort Sarpy was a short-lived trading outpost established in 1837 near the confluence of the Laramie and North Platte rivers in present-day Goshen County, Wyoming. Constructed by Pierre Sylvestre Grégoire Sarpy as a seasonal extension of a broader American Fur Company trading operation, it functioned for only a single trading season before being abandoned. To date, its exact location has not been determined, no archaeological investigations have been conducted at the site, and only two primary historical documents make reference to the post. Fort Sarpy has been, by nearly every measure, all but lost to history.1

Background: The American Fur Company’s Platte River Push

Fort Sarpy’s origins lie in the intensely competitive fur trade arena of the mid-1830s. After John Jacob Astor sold his interest in the American Fur Company in 1834, the St. Louis firm of Pratte, Chouteau, and Company purchased the western division and became the dominant force in the Rocky Mountain fur trade, establishing a strong network of posts throughout the West. In 1836, now operating under the American Fur Company name, the firm decided to expand aggressively into the Platte River region.2 

Painting of a plains landscape, with Indigenous people on foot and horses in the foreground, teepees scattered around a walled fort in the middle distance, by a body of water, and mountains on the horizon
The American Fur Company built Fort Sarpy as a satellite of the same network that operated Fort Union, which was the AFC’s largest and most profitable post. It was located at the junction of the Missouri and Yellowstone rivers on the present-day North Dakota-Montana border. Fort Union’s scale represents the institutional standard behind even a seasonal outpost like Fort Sarpy: the same supply chains, the same accounting, the same St. Louis principals. National Park Service. Click image to enlarge.

They employed Pierre Sarpy and Henry Fraeb as their agents to advance this cause. Sarpy and Fraeb established Fort Jackson on the South Platte in late 1836 or early 1837, in an area that already held Fort Lupton, Fort Vasquez, and Fort St. Vrain. All were within twenty miles of one another, making for fierce competition.3 These posts dealt almost exclusively in bison robes produced by Cheyenne and Arapaho hunters who wintered in the region, and their close proximity reflected the exceptional productivity of the local robe trade rather than poor planning. Fraeb and Sarpy arrived at Fort Jackson with more than $10,900 worth of trade goods, and during the 1837–38 season alone the post took in nearly 2,900 bison robes.4

Construction and Operation

During the 1837–1838 trading season, Fraeb remained at Fort Jackson to oversee operations while Sarpy traveled north to the North Fork of the Platte River—the Fort William area—where he established a small outpost from which to conduct trading for the season.5 This outpost, Fort Sarpy, is known from a contemporary letter by John A. Hamilton placing Sarpy eight miles from B. Woods, who was the Fort William post trader in 1837.6 Hamilton’s letter to Chouteau was largely pessimistic about the season, warning that robes would be very scarce for years to come and describing prospects for the Upper Missouri trade as miserable. It does note that Woods, at Fort William, had run out of goods and that Native Americans in his area were instead going to Sarpy, though Hamilton drew no explicit conclusion about what this meant for Sarpy’s own trade.7 Hamilton’s own role at the firm is not stated in the letter, but its content suggests he was a St. Louis–based correspondent handling accounts and relaying field reports for Chouteau, rather than a trader stationed at a post himself: he writes of using “your surplus funds” at his discretion, and passes along trade news gathered from correspondents across the region.

Painting of plains dotted with people on foot and horseback, with snow-covered mountains in the distance
Alfred Jacob Miller, 'Rendezvous near Green River.' Miller attended the 1837 rendezvous on the Green River in present-day Wyoming—the same season Fort Sarpy was operating on the North Platte—as part of the entourage of Scottish nobleman Sir William Drummond Stewart. The annual rendezvous, where trappers and Native traders exchanged furs and robes for trade goods, was the commercial hub of the same fur trade network that sustained posts like Fort Sarpy. American Heritage Center, University of Wyoming. Click image to enlarge.

Beyond its general location and brief operational record, almost nothing is known about Fort Sarpy. There are no references in the historical record to its size, construction materials, layout, or physical character. All indications are that it was not a permanent post in its own right, but rather a seasonal trading outpost operating as a temporary extension of Fort Jackson.8

One document does offer a glimpse inside the post, though only near the very end of its life. Writing from Fort Sarpy to Pierre Chouteau’s Upper Missouri agent Joseph Picotte on September 27, 1838, trader Louis Howard reported the store almost empty of merchandise: no blankets and no tobacco, only broadcloth, scarlet cloth, and a few other small articles, along with six hundred sixty robes on hand, which he described as very poor quality. Oglala and Shawnee bands wintering nearby told Howard the post was poorly situated and urged that operations move to the nearby post built by Lucien Fontenelle, where there was more grass for horses. Howard also reported fearing that the rival firm of Vasquez & Sublette intended to seize Fontenelle’s post for its own use and had already stationed five hired men there to forestall that.9

Abandonment

Fort Sarpy’s abandonment was tied directly to events further south. Chouteau had grown uneasy about future fur trading prospects in the Missouri and Platte region and was moving his interests elsewhere. Fort Jackson was sold to George Bent and Ceran St. Vrain in October 1838, an event that ended Sarpy’s partnership with Fraeb. Financial pressures, including those brought on by the Panic of 1837, had contributed to Fort Jackson’s closure and, following the transfer, the structure was demolished.10 The sale also effectively rendered the North Platte outpost unnecessary: the American Fur Company had recently purchased Fort William, giving it a permanent presence at the Laramie–Platte confluence and making the small, seasonal Fort Sarpy redundant. There is no indication Chouteau or any of his agents ever reoccupied the post.11 Howard’s September 1838 letter suggests this shift was already under discussion on the ground, independent of the Fort Jackson sale: he had asked Picotte whether Fort Sarpy should be given up altogether in favor of Fontenelle’s post before Picotte’s own arrival.12

After the sale of Fort Jackson, Sarpy returned his attention to his trading business at Fort Bellevue on the Missouri River, where he operated for the next twenty years.13 Fraeb, meanwhile, returned to St. Louis before heading west again with Jim Bridger in the spring of 1840, the two men forming a partnership that led to the construction of a new trading post on the Green River in the summer of 1841, a venture cut short when Fraeb was killed in a battle with Sioux, Cheyenne, and Arapaho warriors in August of that year near the Little Snake River.14

The circumstances surrounding Fort Sarpy’s abandonment reflect a broader economic transformation underway across Wyoming’s fur trade by the late 1830s. Trading posts in the region were rapidly relocating to major waterways and emigrant trail systems to capture the burgeoning bison robe trade and the growing traffic of overland emigrants. The construction of an outpost well away from those developing routes, as Fort Sarpy was, no longer made economic sense.15

What We Know and Don’t Know About Fort Sarpy

Half sheet of lined paper with ornate cursive writing in ink
“To my great surprise, I found the store here almost empty of merchandise… There are now six hundred sixty robes in the store, and even these are very poor quality.” First page of letter from Louis Howard written from Fort Sarpy to Picotte at Fort Pierre on September 27, 1838. Chouteau-Papin Collection, Missouri Historical Society Archives, St. Louis. Published with permission. Click image to enlarge.

Fort Sarpy is documented by only two primary sources: a letter from John A. Hamilton to Pierre Chouteau, Jr. dated December 22, 1837, and a letter from Louis Howard written from Fort Sarpy to Picotte at Fort Pierre on September 27, 1838. Both letters are held in the Chouteau-Papin Collection at the Missouri Historical Society in St. Louis. Beyond these documents, the post appears only briefly in a handful of modern fur trade histories. Its precise location remains unknown, and it is possible the site has been lost entirely.16

If the post’s location is ever identified and physical remains survive, the site could shed light on fur trading activity at a pivotal moment: the late 1830s, when the Rocky Mountain beaver trade was collapsing and commerce was shifting toward the buffalo robe trade and the growing emigrant traffic along the Platte.17 Researchers should note that two separate and better-documented Montana forts also bore the name Fort Sarpy. Both were Chouteau Company posts for trade with the Crow Nation on the Yellowstone River, named for John B. Sarpy, a company partner and nephew of Pierre Sylvestre Grégoire Sarpy, who built the Wyoming post described here. The two forts are geographically and operationally unrelated to this one.18

Footnotes

  1. Greg Pierce, Trading Posts in Wyoming, Multiple Property Documentation Form, National Register of Historic Places, Wyoming State Historic Preservation Office, State Parks and Cultural Resources, Cheyenne, Wyoming, 2012, Section E, 47–48.

  2. Jim Hardee, “The Fur Trade in Wyoming,” WyoHistory.org, November 8, 2014, https://www.wyohistory.org/encyclopedia/fur-trade-wyoming.

  3. LeRoy R. Hafen, French Fur Traders and Voyagers in the American West (Spokane, Washington: Arthur H. Clark Company, 1995), 292; Pierce, Trading Posts in Wyoming, Section E, 47.

  4. Cody Newton, “Native Place, Environment, and the Trade Fort Concentration on the South Platte River, 1835–45,” Ethnohistory 59, no. 2 (2012): 239–260; Cody Newton, “Fort Jackson,” Colorado Encyclopedia, 2026, https://coloradoencyclopedia.org/article/fort-jackson.

  5. J. A. Hamilton, letter to Pierre Chouteau, Jr., December 22, 1837, Chouteau-Papin Collection, Missouri Historical Society, St. Louis; Louis Howard, letter to Picotte at Fort Pierre, September 27, 1838, Chouteau-Papin Collection, Missouri Historical Society, St. Louis.

  6. R. G. Roberson, Competitive Struggle: America’s Western Fur Trading Posts 1764–1865 (Boise: Tamarack Books, 1999), 71.

  7.  Hamilton, letter to Chouteau, December 22, 1837; Howard, letter to Picotte, September 27, 1838.

  8.  Pierce, Trading Posts in Wyoming, Section E, 48.

  9. Howard, letter to Picotte, September 27, 1838.

  10. Newton, “Fort Jackson;” Greg Pierce and Mark E. Miller, “In Search of the Fraeb Battlefield and Trading Post, August 1841,” Plains Anthropologist 60, no. 235 (2015): 227.

  11. Pierce, Trading Posts in Wyoming, Section E, 48.

  12. Howard, letter to Picotte, September 27, 1838.

  13. Hafen, French Fur Traders, 97.

  14. Pierce and Miller, “In Search of the Fraeb Battlefield,” 226–229.

  15. Pierce and Miller, “In Search of the Fraeb Battlefield,” 224.

  16. Hamilton, letter to Chouteau, December 22, 1837; Howard, letter to Picotte, September 27, 1838; Charles Jr. Hanson and Sue Walters, “The Early Fur Trade in Northwestern Nebraska,” Nebraska History 53, no. 7 (1976): 291–314.

  17. Pierce, Trading Posts in Wyoming, Section E, 48.

  18. The Montana Forts Sarpy were named after John B. Sarpy, a Chouteau Company partner and nephew of Pierre Sylvestre Grégoire Sarpy, who established the Wyoming post described in this article. Both were built by Alexander Culbertson as Chouteau Company posts for trade with the Crow Nation on the Yellowstone River: the first (1850–1855) was situated on the north bank about five miles below the mouth of Rosebud Creek; the second (1857–1860) was located about 25 miles below the mouth of the Bighorn River. Activity at the Forts Sarpy is documented by the journal of James Chambers (January 1855–August 1856), held in the Pierre Chouteau, Jr. and Company records (MC 4) at the Montana Historical Society, Helena, and published in Contributions to the Historical Society of Montana, vol. 10 (1940). The two Montana posts share only the Sarpy name and have no operational, geographic, or documentary connection to the post described in this article.