John Wayne was disappointed by the unconvincing studio sets that were used for exterior scenes.

At the film's conclusion, after the credits, we see Kate and Sean standing in their garden waving good-bye. Maureen O'Hara turns to John Wayne and whispers something in his ear, evoking a priceless reaction from Wayne. What was said was known only to O'Hara, Wayne and director John Ford. In exchange for saying this unscripted bit of text, O'Hara insisted that the exact line never be disclosed by any involved parties. In her memoirs she says that she refused to say the line at first as she "couldn't possibly say that to Duke", but Ford insisted, claiming he needed a genuine shock reaction from Wayne. The line remains a mystery to this day.

In the scene where John Wayne discovers Maureen O'Hara in his cottage, the wind whipped her hair so ferociously around her face she kept squinting. John Ford screamed at her in the strongest language to open her eyes. "What would a bald-headed son of a bitch know about hair lashing across his eyeballs," she shot back.

In 1986, the wife of a young New York police officer, who was shot and paralyzed on the job, saw fit to tell reporters this was her husband's favorite movie and that he adored Maureen O'Hara. After reading the report, O'Hara flew to New York and went to the officer's bedside to offer comfort and boost his morale. She became actively involved with the couple during his long recovery and physical therapy, attended their baby's christening and marched in a parade on his behalf.

Charles B. Fitzsimons (Hugh Forbes) and James O'Hara (Father Paul) were the real-life younger brothers of Maureen O'Hara (Mary Kate Danaher).

Continuity

Before Sean enters Mary Kate's home to ask her brother's permission to court her, the flowers he's carrying are very sad looking. After he enters the house, they change into a nice, full, colorful bouquet.

When Thornton and Danaher are at the Widow Tillane's bidding for the cottage, Danaher's highest bid is 710. But in the bar, the accordion player says he heard that Danaher bid up to 810 and nobody corrected him. It is possible that the bidding was longer when originally shot, and edited down, but they forgot to change the scene in the bar.

Towards the end, when all the town folk are along the road waving at the car passing by, the car twice passes by the "IRA" member. He can be seen standing on the side of the road in his bright blue shirt.

John Wayne's wedding ring is clearly visible before he even meets Mary Kate Danaher. It is most clearly seen while he is remembering his mother's words before introducing himself to Michaleen.

When Sean visits Rev. Playfair, the vicar opens his scrapbook to the page which shows the newspaper article declaring "TROOPER THORN QUITS RING. Heavyweight Challenger Hangs Up Gloves After Fatal Knockout. Vows he will never fight again." The article goes on to say: "Trooper Thorn declares he has quit the ring for good and has hung up his gloves for the last time. Thorn's last fight was a knockout over Tony Gardello and so decisive was Thorn's victory that it will be some time before Tony can resume the fight game..."



Factual errors

At the race meeting, two pipers are shown playing. The pipes they are playing are Scottish pipes, characterized by having one bass and two tenor drones in addition to the chanter; traditional Irish pipes only have one bass and one tenor drone, plus the chanter.

When Michaleen's horse stops suddenly in front of the bar, the force should have thrown him forward.

After the wedding, when Sean and Mary Kate are back at the cottage and she storms out, it's dark outside, but the birds are chirping.



Incorrectly regarded as goofs

Michaeleen introduces Sean to Mary Kate as from Pittsburgh, Massachusetts, USA. However, "Steel", "pig-iron furnaces", and "slag heaps" are more generally associated with Pittsburgh, Pennsylvania, USA. (Note: this is an obvious comedic device, showing that Michaeleen is not familiar with US geography.)

After Sean and Red's first confrontation in the pub, the publican is pulling a round of drinks for everyone. It can be seen that he is taking full pints from a line and pretending to fill them. However, in Ireland, it is customary to have a row of drinks, such as Guinness, ready to be topped up, as it is best served once it has settled.

When Sean and Mary Kate are caught in the rain, after a lightning strike, Mary Kate mouths something, but no words are heard. However, Mary Kate is obviously praying to herself when the lightning strikes. Thus, there is no sound to hear.



Revealing mistakes

In the courting scene, the shadow of Michaeleen's pipe can be seen on the painted landscape background.



Miscellaneous

Once the fight scene starts, the old man in the white coat with a can and a limp (John Fitzgerald), can be seen at Danaher's farm when Thorton goes into the haystack. This same old man is seen later on his death bed, being read a war story by the younger Priest. The old man hears the ruckus from the traveling fight, and springs out of bed to hobble after the fight.



Anachronisms

During the station scenes, the locomotive and carriages have the 'Flying Snail' logo of the Coras Iompair Eireann railway company. This logo wasn't introduced until 1944.



Audio/visual unsynchronized

During the fight, the last time Sean gets the bucket of water thrown on him, he is heard to say, "Thanks", but his lips never move.

When the men at the bar sing "Wild Colonial Boy" for the second time, it actually looks like they are singing a different song. Their lips are totally out of sync with the audio/music.

When they are singing "Wild Colonial Boy" for the second time (after Will and Feeney leave), their mouths are moving slower than the song that they're supposed to be singing.

When Sean hops back in the horse cart and says, "Hey! Is that real? She couldn't be!", the sound is out of sync.



Errors in geography

At the horse race there is a sign that says "Inishfree race meet". In Ireland they are called race meetings not meets.

Some of the pipe tunes that are played are Scottish rather than Irish. Whilst it is not uncommon for Scottish and Irish musicians to play each other's tunes, the movie is clearly about Irishness, and so this is no doubt an oversight.



Plot holes

After the horse race, Mary Kate's bonnet is not the only one left. One of the riders knocked down one of the poles holding a mustard-yellow bonnet, and it was trampled by horses and spectators.



Character error

When Mary Kate interrupts the priest fly fishing after storming off, he says that he has been fishing for a particular wily salmon for ten years. Salmon almost always expire after returning to fresh water to spawn (at an age of four years or so), and a keen fisherman would know this.

Michaleen's horse is named Napoleon, but he constantly refers to it as "filly", a term generally associated with a female equine.