Factual error: After Bidwell has his ear bitten off Pratt eventually tries singing Brahm's lullaby into his ear which wasn't written until 1868, but this film is set in 1804.
Factual error: When Chris Farley is climbing up the side of the mountain to return the bird egg, you see the bottom of his moccasins and they appear to be made of a ribbed (for traction) material. Back then, they would have been made from animal hides and the bottoms would have been smooth not ribbed.
Factual error: In the final scene, when Mr. Hunt is planting the flag in the beach, we see the original 13 star pattern, and another larger star in the middle. However, in 1804, there where already 17 states in the union, so the flag should have 17 stars.