I did some more digging this morning and am getting very excited about your ancestor.
You are correct. He died 8 Feb 1929 in Walker, Minnesota. It turns out he moved to Minnesota about 1891 and worked as a clerk for the Indian Agent at Leech Lake Reserve for a number of years. Perhaps that is where he met Childa whom he married about 1892. It turns out she was the daughter of William A. Aitkin (1785-1851), a noted fur trader in Minnesota, and his Ojibwe wife.
G. W. Poussin's father is also an interesting individual. He came to the U.S. early in the 19th century with a letter of introduction from General Lafayette (who had served with George Washington during the American Revolutionary War) commending him as a young French engineer. This was good enough to get him a commission as a captain in the U.S. Army's topographical engineers in 1817. He was promoted to Major in 1829 and resigned in 1832 to become the French ambassador to the United States in Washington, D.C.
I found several letters from the late ambassador asking for a promotion for his son, who you may recall had enlisted as a private in the Army in 1866. It appears that Private George W. Poussin was brought before an examination board for a lieutenant slot, but I assume that he either did not do well in the exam or an opening could not be found (see one of the letters below. Please send me your personal email and I will send you copies of this and the other letters that the ambassador wrote.)
Most importantly for my own research, I found that a collection of Private Poussin's letters from Dakota Territory from Medicine Creek, Fort Sully and Fort Randall have survived. I am in the process of ordering copies and will provide those when I get them. This was an important period on the upper Missouri so hopefully he talks about the Indian treaties and perhaps life in the Army there. Keep your fingers crossed.
Thank you for bringing your ancestor to our attention. I will continue digging to see what else we can learn about him.
Department of State
Washington, 24th May 1867
To the Honorable E. M. Stanton, Secretary of War
Sir:
I enclose a copy of a letter of the 7th instant addressed to me from Paris by William Tell Poussin, Esqr who is presumed to be well known to you. It would afford me pleasure if, compatibly with the public interests, you could do anything towards gratifying his wish in respect to his son to whom he refers.
I have the honor to be, Sir,
Your obedient servant
William H. Seward
13 Rue Tay
Paris May 7, 1867
Wm. H. Seward
Secretary of State, Washington
Dear Sir,
You will I hope forgive me for writing to you about my son George Washington Poussin of the 13th Infantry now residing at Fort Randall, Dacotah Territory. This young man, twenty years old has received a liberal education particularly directed to make him an Engineer. But, after having spent some time in England, he accepted of the situation of an aid engineer to a contractor who had received the mission from an English company to construct railways in the province of Yacatan (Mexico) they embarked for New York on their way to Vera Cruz in July 1866. At their arrival at New York the news received from Mexico were so little encouraging that they were deterred from continuing their journey and decided at once to remain in the United States to search for some useful occupations. In that doubtful situation my son resolved once to separate himself from his chief and to shift for himself; but his enthusiastic feelings for the United States and perhaps also his apprehension for the contingent morrow decided him to enlist with the United States service without seeing or even consulting any of my friends at New York for whom he had letters. A few days after the act, he was directed to the far west and incorporated in the 13th Infantry, Company I 2nd Battalion quartered for the present at Fort Randall Dacotah Territory.
So soon as I received this sad news, I called on my old friend and companion of arms General John A. Dix, United States Minister at Paris who wrote immediately to the Secretary of War recommending my son for a Lieutenancy. The answer from the Secretary of War dated 9th January 1867 was thus worded, “I have directed the name of George W. Poussin to be placed upon the nomination list for a vacancy of that grade in case of his being found qualified”
I am without any news ever since that time, about the result of this special recommendation.
Can you, my dear sir, on my particular consideration and earnest prayer interest yourself so much to the fate of my forlorn son as to promote by your powerful intervention the realizing of my wishes and thus relieve my fatherly anxiety.
Most respectfully and very gratefully your obedient friend and servant
Guillnance Tell Poussin
late Minister from France to the U.S.