Mount Morris needed a hero. Greg O’Connell was available. Like so many small upstate rust-belt towns, it was not prepared for the final quarter of the 20th century. Its manufacturing jobs evaporated. A new Interstate, I-390, bypassed it. Its ambitious kids went away to college and didn’t look back. Its downtown became empty and funereal, thanks to the fluorescent allure of big-box stores like Wal-Mart not far away.

Things began to change in Mount Morris in 2007. That was when O’Connell quietly began buying up buildings — he now owns 20 — on Main Street. For some he paid as much as $140,000. Others he snatched up for $4,000 at tax-lien sales. Then he went to work. He restored the historic storefronts and interiors, cleaning the tin ceilings. He renovated the apartments on the second floors, bringing in fresh paint, oak and maple floors, new windows, nice bathrooms. He spent about $1 million on the properties, he says, and he expects, when all is said and done, to spend another million on renovations.

The results aren’t hard to spot. In 2011 Mount Morris is, tentatively, blossoming. A roomy coffee shop, the Rainy Days Café and Bakery, with gleaming espresso machines, just opened in one of O’Connell’s buildings. (“It kills me that the old guys in town meet to drink their coffee at McDonald’s,” he says.) So has a barbershop, an antiques store and a gourmet food shop that specializes in products from New York State. A deli is scheduled to open soon. Arts groups, he hopes, are on the way.

O’Connell charges these businesses as little as $100 a month in rent, but he asks for things in return. He’s a longtime admirer of Jane Jacobs — he used to carry her classic book, “The Death and Life of Great American Cities,” around like a talisman — and he learned from her and other urban planners. O’Connell’s leases require businesses to leave their lights on at night, to change their window displays at least four times a year and to stay open one evening a week. “If this place is going to make it,” he says, “it’s going to be a community effort.”

The $100 rents he offers, he insists, are not charity. He makes money, too, as much as $500 a month, from the apartments upstairs. In remaking Mount Morris, O’Connell is revisiting his own playbook, the one he used to rehabilitate Brooklyn’s once-deserted waterfront Red Hook area. It was a project that lasted decades, one that put O’Connell on the map and made him a millionaire many times over. Starting in 1982, the year after he retired from the N.Y.P.D., he began buying run-down buildings in Red Hook, then an area known for its drug addicts and prostitutes. He renovated one building at a time, before moving on to the next. He saw the area’s potential before anyone else did and bought his properties — many from the city, which no longer wanted them — at nominal prices. “You’ve got to buy things right,” he says. “You’ve got to be 15 to 20 years ahead of the trends.”