What follows are just the departures from history and not a reflection of the quality of the movie.
From the beginning, William "Curly Bill" Brocius and Johnny Ringo are shown as the leaders of the cowboys. Actually the cowboys were a loose, fluctuating and unorganized group of outlaws with no dominant leader, but Curly Bill did have followers among his associates.
The cowboys didn't wear red sashes as gang colors. One of the movie's two screenwriters, Kevin Jarre, got this idea from Wild Bill Hickok, who occasionally wore one. Some of the cowboys also wore them in imitation of Hickok, but not of a particular color or design. Jarre got the idea of using the sashes to designate membership in the gang from the way L.A. street gangs use colors.
There was no attack on a Mexican wedding party. The rustlers' cattle-stealing raids into Mexico had already caused a lot of tension between Mexico and the United States. Such an attack would probably have either sparked a war or would have forced the President to send in the Army to get rid of Arizona's outlaws. There was considerable cross-border smuggling, during which outlaw Cowboys stole Mexican cattle and ambushed Mexican vaqueros laden with gold on their way to Tucson to buy supplies. In turn, Mexican soldiers ambushed and shot Old Man Clanton and other cowboys.
Wyatt and Mattie did not arrive in Tucson by train and did not meet Virgil, Morgan and their wives there. Wyatt, Wyatt's wife Mattie, his brother James, James's wife Bessie, James's 16-year-old step-daughter, and Doc traveled by wagon train from Dodge City to Prescott, picking up Big Nose Kate on the way. There they met Virgil and Allie. All of them, except for Doc and Kate, then went on to Tombstone with their wagons. Morgan and his wife, Lou, arrived about a month later and then brother Warren Earp arrived several months after that.
There's no evidence Wyatt's second wife, Mattie, was addicted to laudanum in Tombstone, though she did use it later and in fact died from an overdose of the stuff--possibly a suicide.
After stabbing Ed Bailey, Doc is shown stealing money on his way out the door. There's no evidence Doc ever stole anything. According to Wyatt, after repeatedly catching Bailey cheating at cards, Doc finally pulled in the pot without showing his cards, as he had a right to do. Bailey started to pull his gun and Doc quickly stabbed him. The marshal had Doc under arrest in the front room of the hotel, while Bailey's friends were forming a lynch mob outside. In order to save Doc, "Big Nose Kate" Fisher set a shed on fire and while most of the people were trying to put it out, she walked into the hotel and leveled a gun at the marshal, enabling Doc and her to escape.
Wyatt was not dead set against police work, and while he may have turned down some offers of such, he didn't do so for long. Virgil accepted the job of U.S. Deputy Marshal when they stopped in Tucson on their way to Tombstone in November 1879. Within weeks of his arrival in Tombstone, Wyatt was riding stagecoaches as shotgun messenger for Wells, Fargo & Company. Then in July of 1880, more than a year before the gunfight, Wyatt became deputy sheriff for Tombstone under Pima County Sheriff Shibell.
Behan wasn't sheriff when the Earps arrived in Tombstone. In fact, Behan came to Tombstone after the Earps. When Wyatt resigned as deputy sheriff in November 1880, Behan was appointed as his replacement. Then when Cochise County was created in February 1881, Wyatt intended to compete for the position of sheriff against Behan. Instead, Wyatt made a deal with Behan allowing Behan to become sheriff, but Behan didn't hold up his side of the bargain.
Johnny Tyler was a customer, not a dealer, at the Oriental Saloon when Wyatt threw him out. Because of the Oriental's popularity, the competition hired Tyler and a few others to disrupt business there. According to biographer Stuart Lake, Wyatt did haul Tyler out by his ear while Doc held a gun on Tyler's associates. Also, it was Tom McLaury--not Tyler--that Wyatt later slapped. Wyatt slapped him with his left hand while drawing his pistol with his right, saying, "Jerk your gun and use it." Tom didn't, so Wyatt buffaloed (pistol-whipped) him alongside his head and walked away. Wyatt buffaloing Tom is shown later in the film shortly before the gunfight. A month after Wyatt threw Tyler out by his ear, Tyler was back at the Oriental and involved in a confrontation with Doc.
In the movie, Doc is shown looking down on faro. In reality, Doc dealt faro as well as played it--often around the clock. He apparently even preferred it to poker, as did many gamblers at the time. The odds in faro aren't that bad, which is why it never caught on in Las Vegas--the house's share wasn't large enough.
Josie was never a leading actress, though she did travel briefly with Pauline Markham's entertainment troupe playing a supporting role. It was during this time that the 18-year-old aspiring actress met Johnny Behan. Apparently this was before either of them came to Tombstone. The troupe did perform "H.M.S. Pinafore" in Tombstone during the Earp's first week in town but there's nothing to indicate she met Wyatt during this time. Josie returned to her home in San Francisco and Behan eventually sent a marriage proposal to her and she returned to Tombstone to live with him about nine months after her first visit there and about a year before the gunfight.
It is implied in the film that Deputy Sheriff Billy Breakenridge and Curly Bill were gay. In a letter written by Wells Fargo undercover agent Fred Dodge to Stuart Lake in the 1920s, Fred hinted at that Breakenridge might have been gay, but there's nothing to suggest that Curly Bill was.
Behan is shown as not helping City Marshal Fred White when the trouble arose with Curly Bill supposedly shooting at the moon, but Behan was not deputy sheriff at the time--Wyatt was. Apparently several cowboys did the initial shooting, but Curly Bill probably wasn't one of them. As White approached the scene, the cowboys ran around a building. White chased after them and found Curly Bill. He was shot in the groin--not the chest--when he tried to jerk Curly Bill's gun away from him. Only one bullet was fired from Curly Bill's gun and that was the one that killed White. It appears the shooting was indeed accidental and Wyatt even testified in Curly Bill's favor. White died two days after being shot and reportedly said it wasn't Curly Bill's fault.
To add atmosphere, the movie shows a building on fire in the background as the Earps and Holliday walk down to meet the Clantons and the McLaurys. If a building had been on fire, the Earps and probably Holliday would have dropped everything to help put it out.
Josie is shown in Fly's Photograph Gallery having a semi-nude picture taken as the fight breaks out. The semi-nude photograph often said to be of Josie is not really her. It actually dates from 1914 and was widely distributed by the ABC Novelty Company of Brooklyn, New York. Josie was nowhere near Fly's when the shooting took place, but apparently Big Nose Kate was. A woman who later claimed to be Kate said she and Mrs. Fly were looking out the window of Fly's Lodging House when the fight broke out.
In the shootout itself, the movie shows 51 shots being fired in 128 seconds. (One of Doc's shotgun blasts is shown twice from two different angles making it appear he fires three shots from a double-barrel shotgun.) Actually, just over 30 bullets were fired in about 30 seconds.
The lot where the fight took place was only eighteen feet wide, not about thirty, and there were not that many buildings around. The back of the lot was open, though there might have been a low fence. The end of the fight took place out in Fremont Street.
Doc fired the shotgun later in the fight and he only had one pistol, not two.
Morgan wasn't hit in the front of his right shoulder. The bullet entered the back of his left shoulder near the tip of his shoulder blade, traveled across his back and exited about the same spot on the back of his right shoulder.
Ike didn't take Behan's gun and shoot out of Fly's Lodging House, but it is likely that Billy Allen fired at Wyatt or Morgan from his hiding place on the east side of Fly's Lodging House, between Fly's and the assay office. Apparently Wyatt thought Ike had fired from inside of Fly's and he returned fire, which was probably the only shot deliberately fired at Fly's. In reality, Ike had run straight through Fly's and out the back toward Allen Street.
Frank McLaury was not shot in the forehead. Morgan's bullet actually went through Frank's head entering just below his right ear.
Josie and Wyatt probably became romantically involved several months before the shootout and it's very likely she was a high-class call girl at the time.
When Johnny Ringo tried to pick a fight with Doc, Ringo wasn't held back by cowboys. Neither was there any evidence Ringo was drunk. Instead, both Ringo and Doc were disarmed by the police.
The cowboys didn't shoot at the Earp wives or shoot anyone's wife. In the film, Warren says, "They hit Claude's house too, shot up his wife." The cowboys did try to kill Mayor Clum, but he was in a stagecoach--not at his house. Also, a mysterious figure did show up at Virgil's house, but when James Earp answered the door the person said something about having the wrong house and left. The Earps thought this might have been an assassination attempt and they went to stay at a hotel where they felt safer.
Virgil and Morgan weren't attacked right after the fight. The shootout took place on October 26, 1881. Virgil was ambushed on December 28th and Morgan was killed on March 18th of the following year. Wyatt was with Morgan when he was shot and was almost hit in the head by a second shot.
The doctor didn't need to try removing the bullet from Morgan's back because the bullet passed through Morgan and lodged in George Berry's thigh. Morgan also didn't die on a billiard table. The doctor examined him while he was lying on the floor and then they moved him to a couch. He died about forty minutes after being shot.
Virgil and Wyatt did not accompany Morgan's body back to California--their older brother James did. No one was around when Wyatt and three others shot Frank Stilwell beside the tracks near the Tucson train station some distance in front of the train. Stilwell was not killed as he tried to shoot at Virgil and his wife on the train. He was shot apparently after being questioned by Wyatt and his friends. Ike left the scene earlier without a confrontation with Wyatt, though Wyatt and the others searched for him after they killed Stilwell, but couldn't find him.
The vendetta was not carried out in town or in chases or with hangings. Only four cowboys were known to have been killed, though Wyatt hinted there may have been more. These were Stilwell, Florentino Cruz (who might have been the person called Indian Charley), Curly Bill and possibly Johnny Barnes. Cruz was killed after being interrogated and Barnes and Curly Bill were shot in the same gunfight.
This scene is not in the movie. The shootout with Curly Bill did not take place in and across a river. Wyatt and his party rode toward a spring when the cowboys suddenly jumped up from behind a rise and began firing. Wyatt quickly blasted Curly Bill with his shotgun while Doc and the others retreated for cover. The cowboys ran to a stand of willows and the gunfight continued.
An actor was not killed in a stagecoach robbery and Josie was not on a held-up stage.
Sherm McMasters was not killed during the Vendetta and his body was not dragged at Ringo's order to challenge Wyatt. He made it into Colorado with Wyatt.
Doc and Wyatt were in Colorado when Ringo was killed. Doc didn't die in a sanitarium. He died in a hotel.
Wyatt didn't write a booklet about Doc. Wyatt didn't visit him right before he died and didn't even know of Doc's death until eight years later (another site says he found out two months later). Wyatt did write about the gunfight and many other things.
For details, see http://replay.waybackmachine.org/20090627214139/http://www.ferncanyonpress.com/tombston/movie.shtml