Pierre Dorion I: (1740 - 1810)
     He was probably the same Pierre born to Jean-Marie Dorion & Marie-Therese LeNormand, born in Quebec City.  He was married to a woman of the Yankton tribe (a Pierre Dorion married "Holy Rainbow" on the Lower Illinois River in 1780) and their children were:  Pierre (1780/82-1814)(m.Marie Aioe Laguivoise or Wihmunkewakan), Paul (b.abt.1781)(m.Zeah White-Cloud), Louis (b.abt.1782, Illinois), Charles-Martin (b.abt.1783), Antoine (b.abt.1785, Illinois), Thomas (b.abt.1787,Illinois), Perechie (b.abt.1789, Illinois), Marie (b.abt.1791, Nemaha Terr.,Missouri), Jean Bte.(b.abt.1795), Ellen (b.abt.1796)(m.Charles Tackett), Margaret (b.abt.1800, Nemaha Terr., Missouri)(m.Louis Desnoyers, abt.1829 at St.Charles, Mo.) & Comanaka/Comanna (b.abt.1807, Nemaha Terr., Missouri).
     He was apparently living among his wife's tribe from 1785 to 1805 according to one reference and 1773 to 1807 from another source (another source has him settling along the James River in South Dakota in 1775). In 1780 he had corresponded with George Roger Clark, who had organized and led the American military take over of wilderness communities east of the Mississippi River the year before. In 1781 he was trading along the Mississippi & Des Moines Rivers. In July of 1804 Pierre joined the Lewis & Clark expedition, hired as an interpreter, but before the expedition left their wintering site in the spring of 1805, Pierre was sent back to St.Louis with chiefs of the Yankton, Omaha, Oto & Missouri tribes. In 1806, Pierre was commissioned by the U.S. War Department, as sub-agent on the Missouri and western tributaries of the Upper Mississippi River. He apparently died on 23 July 1810 at Petite Rocher, below St.Louis.

Pierre Dorion II: (1780/82-1814)
     He was the son of Pierre Dorion I & a Yankton mother, born in a Yankton village in todays Dakotas. He married Marie Aioe Laguivoise(1786-1850)(also know by Marie Aioe Dorion Venier Toupin) and their children were; Paul (b.1808/09), Jean Bte.(b.1812/13) & an un-named baby born 29 December 1811 while enroute from St.Louis to Astoria on the Pacific coast (this baby died within a month). After Pierre's death she married Joseph Venier and later to Jean Toupin.
     On 29 August 1804 Pierre II is with a large band of Yankton, who meet the Lewis & Clark expedition on the Missouri just above the mouth of the James River when he is mentioned in the expedition journal; "...At four o'clock in the afternoon Sergeant Pryor and his party arrived on the opposite side, attended by five chiefs and about 70 men and boys. We sent a boat for them and they joined us, as did also Mr.[Pierre] Durion, son of our interpreter, who happened to be trading with the Sioux at this time...". In 1809 he served as an interpreter on the Missouri River for Manuel Lisa and in 1811 journeyed west with the land expedition (led by Wilson P.Hunt) of American Fur Co. Lisa obtained a warrant against Dorion in the spring of 1811 for a unpaid debt that Pierre had incurred as a former employee at Fort Mandan. In summer of 1813 he left Astoria with a group led by John Reed to Snake River Country and spent the winter of 1813/14 on the Boise River in Idaho. Gabriel Franchere's journal describes finding Pierre's wife and two boys on the Upper Columbia River while on his return journey to Canada from Astoria. Pierre's wife describes the attack (10 Jan.1814) on Reed's wintering party (which left Reed, Dorion, Jacob Regner, John Hubbough, Gilles Leclerc, Francois Landry, J.B.Turcotte, Andre Lachapelle & Pierre De Launay dead) and her escape the previous January.

Paul Dorion: (1808/09 - 1889)
     He was the son of Pierre Dorion II & Marie Aioe, born according to one source in Beaverhead, Montana. He married 1st.to My-Horse-Comes-Out-Horse (Fasvhimpiimi) & 2nd.to Mary Atoktisau. He died on the Iowa/Sac/Fox Reservation in Doniphan Co., Kansas.

Jean Baptiste Dorion: (1812/13 - 1849)
     He was the son of Pierre Dorion II & Marie Aioe and married Josephte Cayuse/Kiaus in Washington in 1845. He died in Oregon in 1849.

Louis Dorion: (abt.1782 - 1890)
He was the son of Pierre Dorion I & Holy Rainbow, born in Illinois. In July of 1815 he was a signer of a treaty at Portage des Sioux with the Dakota. In 1837 he assisted missonary M.Merrill in translating, "The History of Our Lord Jesus Christ", in to the Otoe, Ioway & Missouri language.

Francois Dorion:
Hired for the 1769/70 season by Maurice Blondeau for la Mer de l'Ouest.

Joachim Dorion:
He was engaged (listed as being from L'Assomption) by McTavish, Frobisher & Co. for the Grand Portage trade in 1797.

Joseph Dorion:
He was hired by la Compagnie du Nord-Ouest for "servir comme Matelot pendant trois ans." (to serve as a sailor for 3 years), in 1798.

Louis Dorion:
Hired by North West Co. for le Bas de la Riviere Rouge, in the 18004/05 & 1805/06 seasons.

Pierre Dorion:
Hired by Jacques & Jean Bte.Baby for Detroit in 1806 (from Trois-Rivieres).

Jean Bte. Dorion:
Hired by James H.Lockwood (American Fur Co.) for the trade above Prairie du Chien for the 1819/20 season.

Battis Dorion Sr. & Jr.:
Both were hired by the American Fur Co. for the trade on the Upper Mississippi River in the 1818/19 season.

Martin Dorion:
     In December of 1835, Kenneth McKenzie, writes Jean Bte.Cabanne from Fort Union, "I have written Mr.Chouteau to engage Martin Dorion, but if you will take the trouble you are much more likely to effect it for me." And in another letter to Messrs.Pratte Chouteau & Co, "I am anxious you should engage Martin Dorion. I cannot say at present whether he will be wanted for this post or the Sioux, of course it will be immaterial to him which post he winters at."
      In September 1836 he was present for a treaty with Zachory Taylor (Colonel in U.S.Army & future President) & the Santee & Yankton.

Pierre Dorion:
     In June of 1839 he joined a party at Ft.Pierre on the Missouri, consisting of Joseph Nicollet, John Fremont, Charles Geyer, William Dickson, Louison Freniere, Etienne Provost, Jacques Fournaise, Francois Latulipe, Joseph Chartran, Louis Zindel, William May, and several others not mentioned, on their way north to Devil's Lake than reaching Lac qui Parle (at Joseph Renville's fort) on August 25. "...joining the party was Pierre Dorion, probably a descendant of "old" Pierre Dorion, Sr., the interpreter who had accompanied Lewis and Clark through the Dakota country..." (from Joseph Nicollet's journal of his 1838-39 expeditions for the U.S. government).
Many thanks to Léonard Dorion for sending the following information on the members of the Dorion Family who ventured to the south-west of Quebec. Léonard has a great deal of info on the family throughout the globe and welcomes inquiries on the family. You can email him at:  leonard.dorion@sympatico.ca

A few words about the Dorion Family in Canada and the United States. Quite a few Dorion's, went down in the United States as early as 1749 and I can follow many others family from New-England out to California. The part that has the most interest for you is this part, maybe you have things on these persons that I haven't got, so you can let me know.
The following Dorion are two brother's:
First Dorion, that I found in Cahokia, Illinois, U.S.A., 3 rd generation in Québec.
Joseph Dorion, born in Québec City , the 19 march 1717 and baptized at Notre-Dame de Québec church the 5 April 1717, father Pierre Dorion and Geneviève Chappau. He passed a marriage contract the 10 august 1749 and got married the 22 august 1749 to Marie Anne Padoka, widow of Louis Pichard ( is said also Padoka Des Ricaras ). She died 24 July 1757 and buried 27 July 1757, in Cahokia Illinois U.S.A. I don't have the information were and when Joseph died and buried and also, if he had any children.
Second Dorion in Cahokia, Illinois U.S.A.
Pierre Dorion, born 26 September 1722, baptized the 28 September 1722. He got married twice,  1st marriage in Québec City 25 February 1743, at Notre-Dame of Québec, to Marie Geneviève Flamand dit Deguise. 2nd marriage to Magdeleine Vige ( in Montréal, Québec the named is said to be Viger ) the 17 august 1773, in Cahokia, Illinois, U.S.A. I don't have where he died or buried and if he have any children.

Two more Dorion decided to join the others in Cahokia, Illinois , they are the children of Jean-Marie Dorion and Marie Thérèse Le Normand ( sometime we see Normand ) two brothers and cousins of the two Dorion previously spoke off.
First: Jean-Marie Dorion, born in Québec City the 18 January 1736 and baptized the 19 January 1736. He was married to Marie Magdelaine Buteau, widow of Alexis Buiette, the 19 November 1773, at the Holy Family Church, in Cahokia Illinois U.S.A. He died the 19 march 1799 and buried 20 march 1799 at the Holy Family Church, in Cahokia, Illinois, U.S.A. I don't know if he had any children.
This is the one I believe you are looking for: Pierre Dorion, born and baptized the 17 January 1740. He married Holy Rainbow, a Yankton Sioux woman around 1779. He died the 10 September 1810 at Fort Osage, Missouri Territory, U.S.A. He had plenty of children.
A bit of history, about Pierre Dorion in the fur trade:

Pierre Dorion married Holy Rainbow around 1779, in Yankton, South Dakota, U.S.A.
1.  Pierre Dorion born around 1780, on the James River, near Yankton, South Dakota. He married Marie Aioe ( also said and written Marie Iowa, Laguivoise, L'auguvoise ) an Indian Iowa woman, born near Scott, Illinois, U.S.A. in 1789.She died the 3rd September 1850 in the Willamette Valley and buried 6 September 1850 at the parrish of St-Louis, in Salem, Oregon , U.S.A. Her Sioux name: WI-HMUNKE WAKAN.
A little bit of information of Marie Aioe. Pierre Dorion, her husband, died the 10 January 1814, on the river bank of the river Bosie, near Caldwell , Idaho, U.S.A.

2.  Paul Dorion, born in 1781, he married Zeah White Cloud.

3.  Louis Dorion, born in 1782, died  the 24 April 1890. Some information on Louis Dorion.
Louis Dorion, son of Pierre Dorion and Holy. He was born in 1782 and died the 29 April 1890. He was married to a native girl. Louis had 2 known sons: Thomas and Louis.
Thomas Dorion ( Sioux name Peguwaakinica ), born 1825, got married 3 times l st marriage to Rattling Iron HIGH-HAWK, 2nd marriage to Good HEART, 3rd marriage to Iron FEATHER.
Louis Dorion, born 1829, he married a girl named Julia, in 1869.
Louis was an interpreter for Chouteau and also Edward. Louis also was  a witness in the following « Treaty ».
l st: Witness to treaty with Sioux of the Lakes, July 19 1815.
2nd: Witness to treaty with Teton, July 19 1815.
3rd: Witness to treaty with Sioux of St-Peter's River, July possibly same date.
You say Louis was hired by the North West Company, for the bottom of the Red River or le bas de la Rivière Rouge, in the seasons of 1804-05 and 1805-06. At that time he was 22 years old, date are fitting quite well.
4.  Charles-Martin Dorion, born in 1783.
5.  Antoine Dorion, born in 1785.
6.  Thomas Dorion, born in 1787.
7.  Perechie (male) Dorion, born in 1789.
8.  Mary Dorion, born in 1791.
9.  Jean-Baptiste Dorion, born in 1795.
10. Ellen Dorion, born in 1796, married to Charles Tackett.
11. Margaret Dorion.
12. Co-ma-na-ka Dorion (Comanaka).

François Dorion:
Born in the 3 July 1735 in Québec City, baptized the 4th July 1735 at Notre-dame of Québec church, son of Pierre Dorion and Geneviève Chappau, brother of Joseph and Pierre. Don't mixed up the Pierre. François spouse is named Louise Galerneau. I don't know when and were he got married for the time being, he had a son named Alexis Dorion, who married Thérèse Bernard the 5 February 1759, at the Immaculate Conception church in Three Rivers ( Trois-Rivières) in the province of Québec. Nothing else on the family.
Maurice Blondeau and François Dorion knew each other since about 1753. Both of them were in the fort Saint-Frederic 1732-1760 ( today Crown Point New-York, NY ). Both of them were godfather of the children of Charles Girard dit Sanschagrin and Catherine Renaud ( François in 1753 and Maurice in 1758. Maurice Blondeau in 1758 was a clerk for the person who was in charge of
the ammunitions ( guns, powder, canons and so on ) of that fort. Source: La population des forts français d'Amérique au 18 siècle, Editions Bergeron, author Marthe Faribault-Beauregard , page 29 , tome 1.

Now a little bit of history on Peltier-Antaya family.
In the Dorion research there is one Pierre Peltier-Antaya, I believe they were half-breed Indian, I will tried in the near  future to gather more information on that  family, for the time being:
« Marie Josephte Dorion, daughter of Noel Dorion and Marie Josephte Normand was born the 21 march 1772, baptized the 22 march 1772. She the 4th generation of Dorion in Québec city. She married Pierre Peltier-Antaya , son of Jean-Baptiste Peltier-Antaya and Catherine Vole. The Vole family I believe it to be Indian also. Will let you know. They married the 24 April 1797 in St-Mathieu de Beloeil, Province of Québec».