[6]: 10 As a boy, Henry Sibley was educated at the Academy of Detroit, after which he was tutored privately in Latin and Greek for two years by Reverend Richard Fish Cadle, an Episcopal clergyman and classics scholar.

Sibley later wrote that he was finally persuaded by Dousman's glowing description of the Minnesota Valley as a hunter's paradise[9] where "woods abounded with bear, deer and other game animals, and the numerous lakes with aquatic fowl of every variety.

After spending several days at the American Fur Company's Western Outfit headquarters at Prairie du Chien, Sibley traveled the remaining 300 miles of wilderness by horseback.

From 1836 to 1839, Sibley was in charge of operating the army sutler's store at Fort Snelling,[14] in partnership with Pennsylvania newspaper editor and former Indian agent Samuel C. Stambaugh, who had been appointed to the post but had no interest in moving there.

[6]: 51 In 1835, Sibley started lobbying for the establishment of a post office at Fort Snelling with regular service from Prairie du Chien, contacting his political connections in Michigan Territory for support.

[6]: 66 However, in the summer and fall of 1837, the United States government signed three major treaties with the Ojibwe, Dakota and Winnebago tribes, in which they agreed to give up all their lands east of the Mississippi River in return for compensation.

"[6]: 66  In December 1836, Sibley had written to American Fur Company president Ramsay Crooks urging him to lobby his Washington connections to prevent Indian agent Lawrence Taliaferro, a long-time political enemy of the traders, from being appointed as treaty commissioner the following year.

[15] However, Taliaferro prevented most of the American Fur Company traders from entering the room where discussions took place between Secretary of War Joel Roberts Poinsett, Commissioner Carey A. Harris, and the Mdewakanton chiefs, starting September 21.

[19] The traders were "jubilant" over the terms of the treaty, and Sibley wrote to his father saying that once his debts were paid, he hoped to end his relationship with American Fur and return to Detroit the following year.

[6]: 67–68  In November 1839, the Western Outfit partners including Henry Sibley agreed with Ramsay Crooks to extend their original contract with American Fur Company for another year, until August 1, 1841.

[8][9] However, as he descended the hill, he was "disappointed to find only a group of log huts" occupied by the fur traders and staff, and included an urgent request for new buildings in his first letter to Ramsay Crooks on November 1.

Monsignor Augustin Ravoux, a Catholic missionary, baptized "Hélène," daughter of Tahshinahohindoway and an unnamed father, with fur trader William Henry Forbes named as her godfather.

She appointed roughly two dozen "lady managers" to assist fundraising efforts for the historical preservation of Mount Vernon, including Mary LeDuc and Rebecca Flandreau, who would succeed her.

The advisory board also included many of Henry Sibley's business contacts such as Richard Chute, Alexis Bailly and Martin McLeod, and family friends such as John S. Prince and William Gates LeDuc.

[32] In 1847, Dousman and Sibley, together with Henry Mower Rice, Bernard Brisbois and others, purchased shares in a packet company with steamboats running on a regular schedule between Galena, Illinois and ports in Minnesota.

From Pembina, Kittson sent large trains of carts along the "Plains Trail" west of the Red River and down the Minnesota valley, well-defended against possible attacks by Dakota hunters who were resentful of the whole slaughter of buffalo by the Métis and had threatened to stop any goods from going across their country to the north.

From this time onward, Sibley and Kittson proceeded to build a thriving business in supplying the British troops with everything from champagne to sheet iron stoves, transporting goods up the Red River Trail.

In 1846, drought and the failure of the corn crop made things worse, particularly among the Sisseton and Wahpeton bands, and traders including Martin McLeod and Norman Kittson had to extend credit to the Dakota in the form of food.

By 1848, a ring of Dakota including Little Crow had become so successful in trading whiskey for fur skins that Sibley and McLeod were compelled to set up river patrols to stop any canoes carrying contraband to the west.

[6]: 99 Henry Sibley was initiated into public life as a young man in Michigan Territory when he received his first commission as justice of the peace of Mackinac County from Governor George Bryan Porter.

[36] In 1840, Sibley was called upon to hear a criminal case involving the brutal rape of a ten-year-old girl which took place in Wisconsin Territory, because justice of the peace Joseph Brown was away at the legislature in Madison.

[6]: 78 Following the defeat of Jacksonian Democrat Martin Van Buren in the 1840 United States presidential election, the new Secretary of War John Bell moved quickly to try to purchase land from the Dakota.

[6]: 80 Much to the surprise of Henry Sibley and the partners of the American Fur Company's Western Outfit, John Bell appointed Governor James Duane Doty of Wisconsin Territory to negotiate a treaty with the Dakota to acquire 30 million acres of land on behalf of the U.S. and require their settlement in farming communities as part of a plan to grant citizenship.

[6] On July 31, 1841, Governor Doty concluded a treaty with the Sisseton, Wahpeton and Wahpekute in Traverse des Sioux, with assistance from Alexis Bailly as secretary, although several major chiefs including Sleepy Eyes and Burning Earth did not participate.

[6]: 81 On August 4, 1841, Doty concluded a similar treaty with Mdewakanton in Mendota, and then left, tasking Sibley and Hercules L. Dousman with securing signatures from chiefs Wacouta and Wabasha III, who had refused to attend the signing.

[6] In January 1842, Ramsay Crooks sent Henry Sibley to Washington to serve as the chief manager of the lobbying effort for the Doty Treaty, reminding him that the future of the Western Outfit "depend[ed] very much" on its ratification.

In the fall of 1847, Sibley wrote to his friend Charles Christopher Trowbridge regarding the Winnebago:"These poor fellows will be thrust between the powerful contending tribes of Sioux and Chippewas, and I fear they will fare badly...

The tale of how he rose, polished and urbane, before a Congress that had expected a figure in buckskin and eloquently defended the right of pioneers to the protection of government and law became — almost immediately — Minnesota's most cherished founding legend.

[50] The remaining 300 Dakota warriors were imprisoned and more than 1,600 non-combatants: women, children and elderly were held in a crowded encampment on Pike Island below Fort Snelling until river transportation resumed in the spring .

In 1874, Governor Cushman Kellogg Davis asked Sibley to administer the distribution of $19,000 in funds raised for the relief of settlers worst affected by the grasshopper invasion, working with John S. Pillsbury of Minneapolis.