When I first contacted Delia Barry, she asked to be called back later. It was a Wednesday afternoon in Greystones, Ireland, where she lives, and she was playing bingo. “It’s just more of a social gathering for local senior citizens, which I am one of,” Ms. Barry, 83, said by telephone.

When not at bingo, Ms. Barry is usually knitting. Four of her sweaters appear in the Oscar-nominated film “The Banshees of Inisherin,” which is set on a fictional island in 1923, toward the end of the Irish civil war. These include a navy roll-neck and a red pullover with a distinctive long collar, both worn by Colin Farrell; a thick blue knit worn by Brendan Gleeson; and a purplish ribbed fisherman’s sweater worn by Barry Keoghan. Esquire U.K. called “Banshees” the “Next Great Knitwear Film.”

Ms. Barry received a shout-out in the film’s credits, for knitwear, and her story has since gone viral on Instagram and TikTok, where teenagers and 20-somethings have shown off their attempts to recreate her designs.

“It’s pure madness,” she said of the attention. “I’ve knitted so many jumpers, they are just another jumper to me.” She hopes to see the film a second time soon, she said, to better appreciate the acting and Martin McDonagh’s direction. “When I went the first time, I was just looking for the knitwear,” she said.

Ms. Barry learnt to knit at school in Cahir, County Tipperary, at age 7. As a teenager, she made her own clothes, trying out new patterns, perfecting shapes. At 20, she moved to London with her future husband and worked in a telephone factory. More than a decade later, they returned to Tipperary, where Ms. Barry worked in a bar before moving to her husband’s birthplace of County Wicklow, where the town of Greystones is.

“Here is where I’ll be staying now,” she said. “I won’t be moving again.”

Ms. Barry knitted throughout her marriage, she said, but her commitment grew when her husband died in 2010, and she began knitting to raise funds for Greystones Cancer Support. “They were very good when he was diagnosed,” she said. She donated a portion of her film earnings to the organization. “You never know when you’re going to need them,” she said.

On an average week, Ms. Barry rises at 6 a.m. and knits until 8.30 a.m. She always knits in the same spot — on her sofa, with the light from the window behind her. At 9.30, she goes for a walk to the beach with a friend, about two miles away. She has never owned a car, she said, and has walked everywhere her whole life. (She has also never used email.)

They’ll get a coffee and watch the sea for an hour. Back home, she’ll knit for another three to four hours. She’ll take a short break for dinner, then knit throughout the evening. “I get up and walk around every so often,” she said.

Knitting is therapeutic for Ms. Barry. “When you’re living on your own, it’s nice to have something to do,” she said. She knitted the sweaters for “The Banshees of Inisherin” during one of Ireland’s pandemic lockdowns, spending a week on each. “It kept me sane,” she said.

Ms. Barry said she was sad that young people today don’t learn knitting in school. She and her husband had no children on their own, but they helped raise her nieces and nephews when her sister died unexpectedly. Her younger relatives have followed Ms. Barry’s viral fame with amusement. “They say: ‘You’re not going to know us now. We’ll have to make any appointment just to talk to you.’”

Eimer Ni Mhaoldomhnaigh, the film’s costume designer, commissioned Ms. Barry to create the sweaters. After the release of the movie, Ms. Ni Mhaoldomhnaigh recalled, “My daughter, who is 20, came and said Delia is a TikTok sensation.”

Ms. Ni Mhaoldomhnaigh came across Ms. Barry’s work when she was sourcing knitwear for a 2017 television adaptation of “Little Women.” A woman working on the production knew that Ms. Barry had helped on other films, including “Dancing at Lughnasa,” for which she created knitwear for Meryl Streep’s character.

“Ireland is very small,” Ms. Ni Mhaoldomhnaigh said, laughing. “It’s all word of mouth.”

Ms. Barry credits her success to being willing to take on a job without a pattern, something many knitters would be wary of. For “The Banshees of Inisherin,” Ms. Ni Mhaoldomhnaigh provided photographs of Irish fishermen from the 1920s, which Ms. Barry studied with a magnifying glass. One showed a sweater with a distinctive long collar, the inspiration for the red piece that would become Mr. Farrell’s.

“We were really lucky to be able to make all the costumes for the principal characters,” Ms. Ni Mhaoldomhnaigh said. “Not just the knitwear, but the tailoring, the hats.” Ms. Barry is not the only older figure involved: Ms. Ni Mhaoldomhnaigh’s tailor is well into his 80s. “I say every day, what are we going to do if he ever retires!” she said.

Once each item was complete, it went to the aging department, where pieces are dyed and distressed. “People think they just take a cheese grater to it, but it’s not as simple as that,” Ms. Ni Mhaoldomhnaigh said. She sees the process as a means of communicating subtleties about a character — somebody who walks purposefully with their hands wedged in their pockets, somebody who gets nervous and wipes their hands on the front of their clothing.

Ms. Ni Mhaoldomhnaigh theorized that Mr. Farrell’s on-screen sister, Siobhan (played by Kerry Condon), would have made his red sweater. “These were very much day-to-day activities at that time — knitting, making, darning,” she said. “Siobhan would have thought, “Well. Mammy and Daddy are dead, and he’s my little brother, and I’m going to look after him, and I want him to look good, so I’ll put a collar on it as a little touch.”

Ms. Ni Mhaoldomhnaigh saw the piece as a gesture of love and protectiveness. Wrapped up in that collar, and the boyish length of it, were Mr. Farrell’s character’s innocence and naïveté, which are essential to the film’s plot.

Mr. Farrell himself was skeptical of the sweater at first, worried about the fit, Ms. Ni Mhaoldomhnaigh said. So Ms. Barry started afresh. In the end he loved it. “With an item like that, you really have to sell it to the actor,” Ms. Ni Mhaoldomhnaigh said. “He has to believe that his character is going to wear this.”

The film has been praised for the way it deals with masculinity, friendship and loneliness, but aging is also a theme, especially the fear that one has not made enough of one’s life. In one scene, Mr. Gleeson stands before Mr. Farrell and says, “I just have this tremendous sense of time slipping away from me.” Ms. Barry identifies with that sentiment.

“This is all coming too late for me,” she said. “I do think if this had happened maybe 20 years ago it would have been nice.”

Still, she added, “I’m not passed it yet.” Her recent success has made her feel valued, she said, and she is already at work with Ms. Ní Mhaoldomhnaigh on pieces for a new film.

“Because you get older, it doesn’t mean that you’re not useful anymore,” Ms. Barry said. “There’s a lot we can do, if we want to.”