Factual error: In the third chapter of the movie, as the Union soldiers run into the Crater, they are flying the fifty-star American flag which is not the correct flag for the time period. The flag, if it is counting all states, even Confederate states at that time, should have 35 stars. A star for West Virginia, which seceded from Virginia during the American Civil War, was added to the flag in 1863.
Factual error: Women of rural areas in 1864 did not shave their legs to the extent shown throughout the movie. For example, when Inman is seduced by the man's wife and when he's having sex with Ada, you'll notice both women are very clean shaven. Even if they had shaved, they didn't have such precise shaving tools back then.
Factual error: Inman appears to be hospitalized in some capital in late summer of 1864. The capital cannot be Richmond, which is under siege, so it must be Raleigh. In the hospital's yard are well-dressed ladies having tea and slaves picking cotton, both of which are highly unlikely in the final months of the war. Raleigh is quite a distance west of the North Carolina coast, and Cold Mountain is at least 250 miles almost due west of Raleigh. Yet, Inman went east to the coast. In the very next scene after wandering on the coast, he has somehow arrived in the mountains, which are less than 50 miles from Cold Mountain in Haywood County. Thus, the majority of his adventures had to have taken place in the last 50 miles of his quest, which is not what is implied by the plot.