Another dozen Dunkin' Donuts restaurants are coming to Denver.In February, Sizzling Platter LLC said it planned to open 11 Dunkin' Donuts locations in Denver. Sizzling Platter operates 124 restaurants, including Little Caesars, Sizzler and Red Robin Gourmet Burgers, in seven states.In March, the donut company signed a multi-unit store development agreement with the father-daughter team of Doug and Katy Redman for seven restaurants in Denver. The first is planned to open in 2013, and all should be open by 2018. Doug Redman has experience owning Subway restaurants, electronics stores and taco restaurants.Now a third franchisee, Buzz and Brad Calkins, has announced plans to open 12 new restaurants in Denver. The first restaurant is planned to open in 2013, and the remainder by 2018.The Calkins are members of a long-time restaurant family. Four generations of Calkins have owned and operated multi-unit gas and convenience operations in three states.That means Denver will have more than two dozen Dunkin' Donuts stores opening in the next six years. Krispy Kreme has two locations in Lone Tree and Thornton. LaMar's donuts has 11 locations in Colorado. Winchell's has 12 locations in Colorado."There can never be too many locations," said a Dunkin' Donuts spokeswoman.Dunkin' Donuts started in 1950 as a place for coffee and donuts. Now it's expanded its menu to offer bagels, muffins, sandwiches, hash browns and more.