Fort Hall, according to the lady who worked at the replica the morning I went there, was a way station for travelers on the Oregon Trail near Pocatello. It was never a military fort. So, it was like a 19th century equivalent of a truck stop! It was built as a commercial venture by a man from the East Coast; forgot his name. He wasn't Mr. Hall. Mr. Hall had something to do with funding the fort, but never personally set foot there.
Shortly after it was built, Fort Hall was taken over by the Hudson Bay Company. It was a planned takeover, much like how big corporations take over small businesses today!
Fort Hall has been destroyed. The site wasn't discovered until just 8 years ago! It's somewhere in the Res, as the Indians call their place. Now there are occasional excursions out there from Pocatello. There's one this month, but I don't remember when.