Anne Saxelby, a pioneer in championing fine American cheeses at a time when cheese lovers largely looked to Europe for such artisanal products, died on Saturday at her home in Brooklyn. She was 40.

The cause was a heart condition, said her husband, Patrick Martins, an owner of Heritage Foods USA, a purveyor of meat and poultry from independent American farmers.

In 2006, when Ms. Saxelby opened Saxelby Cheesemongers, the American cheese industry was largely just that: industrial and mass market. Her shop was a daring enterprise that carried only American-made cheeses from small producers.

The space was hardly more than a nook with a refrigerator in the original Essex Market on the Lower East Side of Manhattan. Almost immediately, Ms. Saxelby attracted attention among cheese lovers, and especially among chefs in the growing farm-to-table movement.

In 2017 she opened another store in a more spacious location in Chelsea Market, keeping the Essex Street spot until that market closed in 2019. With a business partner, Benoit Breal, she also opened a warehouse space in the Red Hook section of Brooklyn.

News of Ms. Saxelby’s death resonated throughout the food world.

“Her passion for celebrating American farmstead cheese influenced a generation of cheese makers, chefs, cheese enthusiasts and friends and changed the way we engage with American foods,” Michael Anthony, the executive chef of Gramercy Tavern in Manhattan and a regular customer, said in an interview.

Steven Jenkins, a former cheesemonger at Fairway Market, said in a statement: “Anne Saxelby was the U.S. ambassador for American cheese makers and their handmade cheeses. Her yearslong, tireless effort to promote them and make them mainstream will forever have its effect, and will long be remembered.”

Anne Therese Saxelby was born on March 25, 1981, in Dayton, Ohio. She grew up in Libertyville, Ill., a northern suburb of Chicago, to Bill Saxelby, an entrepreneur, and Pam (Reesman) Saxelby, a children’s book author.

Bill Saxelby said in an email that his daughter’s interest in cheese started when she was young. The family’s “classic Midwest” cheese knowledge was limited to Kraft singles, he said, but while Anne was studying at Libertyville Community High School she wrote a thesis about decay and fermentation, a cornerstone of cheesemaking. She moved to New York in 1999 to attend a studio art program at New York University’s Steinhardt School.

Her introduction to American cheese makers came in 2003, after art school, when she met the people who ran Cato Corner Farm in Colchester, Conn., and began working there, where she learned to make raw milk cheese. From there, her career picked up speed.

She worked for a year at Murray’s Cheese, one of Manhattan’s premier cheese shops, where “she was among the most talented of those I trained,” Rob Kaufelt, the store’s former owner, said in an email.

Her next move was to Europe. She interned in Paris with Hervé Mons, a cheese master, and then worked on farms in France and Italy to learn about goat and sheep milk cheeses, picking up fluency in French, Italian and Spanish along the way.

But she was convinced that American cheese producers were capable of competing with Europeans. She started her business with money from her father, who said that after just six months the store had a positive cash flow. Three months after that, she was able to pay herself a salary. Mr. Saxelby said she choose Essex Market as her first location because she believed strongly in supporting community initiatives.

She was an advocate for dozens of farms, putting many of them on the map and their names on shopping lists.

She was an early supporter of Jasper Hill Farm in Greensboro, Vt., which opened just a couple of years before she started her business, and she helped introduce their wheels and wedges to many chefs. She collaborated with the farm on a prizewinning Alpine-style cheese called Calderwood, which she introduced at her store.

“We grew up in cheese together,” Mateo Kehler, who started Jasper Hill Farm with his brother, Andy, said by phone. “Thanks to her, our cheeses are on menus all over the city.”

Dan Barber, the executive chef and an owner of Blue Hill at Stone Barns in Pocantico Hills, N.Y., and Blue Hill in Manhattan, said that soon after Ms. Saxelby opened her store he offered a cheese plate on the menu with three classic European cheeses, like Beaufort, tomme and Vacherin, paired with three American cheeses.

“Anne’s excitement for this plate was palpable; in the end I called it the Saxelby cheese plate,” he said by email. “She said that the pairing was a great way to talk not just about the emergence of American cheese, but how our cheesemakers were building on traditions and creating new ways to express old ideas.”

In addition to her husband and father, Ms. Saxelby is survived by her mother; a son, Max Martins; two daughters, Reggie and Josie Martins; a sister, Megan Saxelby; and a brother, Bill.

During the coronavirus pandemic Ms. Saxelby led virtual cheese tastings, sending tasting kits to participants. The store also sells crackers, charcuterie, condiments, beer and cider. (However, Mr. Martins said, Ms. Saxelby never considered carrying vegan or nondairy cheese.)

Mr. Breal, her business partner, said the company would continue to move forward, “one step at a time,” adding, “We plan to continue our mission to be the bridge between local cheese makers and the consumers for many years to come.”