Given the choice between living in a tiny Toronto shoebox in the sky or a sprawling space in a small riverside town, Natasa and Cory de Villiers chose the option that made the most sense.

They moved into a 3,000-square-foot commercial building in Hespeler, a Southwestern Ontario town that is part of Cambridge.

"When we first moved here we had no idea where we were moving. We literally saw this really affordable building in a small town that was off the 401," Ms. de Villiers said. "It was far cheaper than anything we could even think about moving into in Toronto. It just made more financial sense."

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The same kind of math led to Cassie McDaniel and Mark Staplehurst leaving Toronto for Paris, Ont. Although neither had ties to the town, as new parents who could work remotely, they felt its lure. "We came out here a few times and it just clicked. It's beautiful. There's no traffic. You don't have to fight for a spot when you sit down for coffee," Ms. McDaniel said. "… It just made sense for us and the kind of lifestyle we want."

That lifestyle now includes booming businesses that neither had intentions of starting when they moved; people like them are transforming small-town business in a broad swath of towns that dot the Greater Golden Horseshoe – a stretch of Southwestern Ontario counties ringing the outer GTA from Niagara in the west to Northumberland in the east.

"There's a whole cadre of people coming in. … They're offering goods, services and opportunities that are unique for the area but may not be in downtown Toronto," said Paul Emerson, chief administrative officer for the County of Brant, which includes Paris. "They can really capture a market here without the same type of competition that they would see in downtown Toronto."

Paris has a population of about 12,000 people but is poised for fast growth: More than 3,000 new housing units are being built, Mr. Emerson said.. While real estate is still cheaper than in Toronto, the average price of homes sold in April reported by the Brantford Regional Real Estate Association, which includes Paris, was $418,636, up 25.9 per cent on a year-over-year basis. "It's not the same small town now," Mr. Emerson said. "People who may have located in bigger cities 10 years ago to start their business … are seeing the opportunities available in this area."

When Ms. McDaniel, an Orlando native, and Mr. Staplehurst, raised in Luxembourg, moved to Paris, they both worked in Web design; Ms. McDaniel intended to telecommute to a city-based job. But one thing led to another and the couple's own digital agency, Jane and Jury, was born. "We are just entrepreneurial and like having our own products," Ms. McDaniel explained. Their clients are located all over the world, Paris, Ont., included.

"We draw from our experience in the city and the contacts we made there, but we have made a name for ourselves locally," Ms. McDaniel said. "There's no one else out here that really has the same skill set. That's definitely a bonus. There's enough competition to feel inspired, but not so much that it's overwhelming or intimidating."

In Galt, another town that is part of Cambridge, Graham and Monica Braun had a similar experience when moving from Montreal with their young family. Mr. Braun, an IT consultant, and Ms. Braun, who worked in the pharmaceutical industry, decided to see if they could transform Mr. Braun's hobby of roasting coffee beans into a wholesale business aimed at retail coffee shops. When they opened Monigram in 2013, they had a small retail space so people could taste what they were buying. Then demand exploded.

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"We were run off our feet on the retail side," Mr. Braun said. "People were coming in and drinking cup after cup." The couple reversed the course of their business and decided to focus on their coffee shop; the wholesale arm took another year to grab their focus.

"You just chase whatever is working," Mr. Braun said. Four years later, the shop is still going strong. Had the couple settled in Toronto, though, it would never have been. "I'm not sure if we would have become entrepreneurs there," Mr. Braun said. "We just feel plugged into the community here in a way that I don't think we would in Toronto."

Ms. de Villiers, a former college instructor who runs O & V Tasting Room, an olive oil tasting room and specialty food store in Hespeler, has the same sense. "The costs would be so high in Toronto that it wouldn't be worth it," she said. "Here, you make more of an impact. You open a business and your presence is felt – it's a big change to a small community."