A few days after the New Year’s holiday, clerks at the Dollar Tree store in the St. Paul, Minn., Midway neighborhood were busily setting up new displays celebrating Valentine’s Day and Super Bowl Sunday. Any remnants of the Christmas holiday season were long stowed away, and the bright new merchandise enticed shoppers anew.

No longer dusty, out-of-the-way haunts, dollar stores have grown into a $56 billion industry, a 43 percent increase since 1998, according to the industry research firm IBISWorld.

One of the few niches of retail expanding in a dim economy, the dollar store industry’s four top players – three of which are Fortune 500 companies – are no longer snubbed by developers, landlords, investors and consumers because of their perceived working-class customer. Publicly traded Dollar General, Dollar Tree, Family Dollar and 99 Cents Only Stores are expanding rapidly – so much so, a recent report by Colliers International found, that there are more dollar stores nationwide than drugstores, a profound conclusion given the nation’s aging population.

Dollar stores have responded to the new value-obsessed consumer by providing a brighter, cleaner retail experience with a dependable, well-edited selection of goods, including many food items, some perishable like milk and eggs.

Dollar chains are opening hundreds of new locations. This is a fortuitous development for commercial real estate brokers. As national retailers such as Borders, Linens ‘n Things, Ultimate Electronics and others shut their doors, landlords have struggled to fill empty space in their shopping centers. Dollar stores often fill the void.

All of the chains emphasize convenience when looking for new space. Typically, they rely on automobile counts on nearby roads as a way of winnowing down potential sites, according to the Colliers report, while other retailers fervently study a potential market’s demographics. In competitive markets, the success of a dollar store often depends on storefront visibility and the impulse shopping urge that it encourages.

“Dollar store success depends on the power of the spontaneous purchase,” said Andrea Christenson, vice president at Cassidy Turley, a Minneapolis-based real estate firm. “You may not need anything going in, but you develop a need once you’re inside.”

Dollar General recently announced that it would open 625 more stores this year – almost two a day – across the country, said Tawn Earnest, spokeswoman for the Tennessee-based chain. She declined to be more specific. Dollar General is the largest chain nationally with more than 9,800 stores.

Historically, Dollar General has opened in rural areas that were so sparsely populated that even Walmart passed. Today, 70 percent of the stores serve communities with fewer than 20,000 residents, according to its annual report. Customers typically live within three to five miles of the store – within a 10-minute drive – and they shop in the store an average of 10 minutes.