Farms in Chester County, Pa., produce 400 million pounds of mushrooms annually. That’s about half of all mushrooms grown in the U.S. They’re grown indoors in long, gray cinder-block houses built into the side of a hill.

Farms in Chester County, Pa., produce 400 million pounds of mushrooms annually. That's about half of all mushrooms grown in the U.S. They're grown indoors in long, gray cinder-block houses built into the side of a hill.

Farms in Chester County, Pa., produce 400 million pounds of mushrooms annually. That’s about half of all mushrooms grown in the U.S. They’re grown indoors in long, gray cinder-block houses built into the side of a hill.

Four hundred million pounds of mushrooms come from farms in Chester County, Pa.