Then and now, the most compelling sight in the town was its white steeple church. The town was part of the land owned by William Penn, the Quaker who also founded Pennsylvania. In the background, the music from Los Bukis, a Mexican band, played, as we gathered outside one of the shacks, next to a fire, waiting for grilled cabrito (goat), tortillas and jalapeños. I was appalled by their poor living conditions — rundown trailers and outhouses tucked into the landscape, as if they weren’t part of the town.

The men talked about leaving. They didn’t integrate, much less assimilate. Most were desperate to reunite with their families back home. Thanks to President Ronald Reagan’s landmark Immigration Reform and Control Act, though, an estimated 2.7 million people were legalized beginning in 1986, enabling Mexicans and other immigrants to roam freely in greater numbers in search of opportunities.

In Kennett Square, instead of leaving as they had originally hoped, the men saw the value in an industry that provided year-round work. In rural America they saw the ideal place to raise a family. Today, about half of Kennett Square’s residents are Hispanic, of whom an estimated 80 percent are Mexican, according to La Comunidad Hispana, which provides medical, educational and legal services for immigrants.

For more than three generations, the newcomers have contributed to the renewal of Kennett Square. Some Mexican immigrants have started their own mushroom farms. Some own hair salons. Others own Mexican grocery stores. There’s even a taco war, as locals debate who makes the best tacos: Are they downtown or in nearby Avondale? Hundreds of children are now high school graduates, and many went on to earn college degrees.

“The Mexicans changed the community for the better,” Loretta Perna, program coordinator of the Walk in Knowledge Program at Kennett High School, told me. “They became part of not just the mushroom community but part of the overall community, bringing color, richness to an otherwise bland life.”

One of Ms. Perna’s students is Sofia Soto, 18, daughter of Jaime Aguilera, a veteran mushroom worker who built his own landscaping business. Mr. Aguilera now sits in a detention center, waiting for an immigration judge to decide his fate, that of his family and in a more general sense, the future of his adopted hometown. Ms. Soto, like her two siblings and her mother, is an American. She’s determined to attend West Chester University this fall, a promise she made to her father. But she said: “If he’s deported, it won’t be easy. He’s my inspiration.”