Fast-growing OtterBox is expanding its real-estate footprint yet again, with plans for a new building in downtown Fort Collins based on expectations its payroll will grow from 400 today to as many as 1,500 in the next three years.

In a quiet deal that closed in October, the electronics case manufacturer purchased a seven-story building at 315 Oak St., a locale known as the Rocky Mountain Building, for $927,000, according to Larimer County public records. The building now houses 60 “Otters,” as well as three startup companies formed by former OtterBox employees.

In the same entrepreneurial spirit that began OtterBox, company CEO and founder Curt Richardson, along with President Brian Thomas, have invested in the ideas of a handful of Otters with their own business-launching aspirations. Nerdy Minds Marketing, Wild Rock PR and 1OAK Technologies are all offshoots of OtterBox’s success, run and staffed by former OtterBox employees and supported by OtterBox’s executive team in a variety of ways.

The purchase of the Rocky Mountain Building is only the beginning of OtterBox’s growth plans for the next few years.

Also in the works is another building just across the street from its 52,000-square-foot headquarters at 209 S. Meldrum St., which was completed in the summer of 2011. A new, 53,000-square-foot, five-story building is making its way through the city’s permitting process, and, upon approval, should break ground by fall. The property’s address is 331 Meldrum St.

The company hopes to have employees moved into the new building within 18 months, according to Thomas, and when the building is complete, he estimates, it will be at capacity.

There are still more plans in the works for housing Otterbox employees, to be put in motion when construction on the new facility is finished. The Rocky Mountain Building will be renovated, Thomas said, and additional buildings will be constructed near it.

Supply-chain management and IT are two of the departments experiencing the most growth, as is customer service. There are currently 65 positions open at the company, according to Thomas.

The company’s expansion has shown no sign of slowing; it added 55 people in the first quarter compared to 16 in the same period last year.

Ultimately, the plan is to create a “campus” in downtown Fort Collins that will allow for connectivity between employees in different buildings, as well as easy access to downtown amenities that will not only benefit OtterBox, but bolster business for downtown restaurants and other retailers, according to Thomas.

OtterBox has also leased two spaces with the option to purchase just to the west of the Rio Grande Mexican restaurant at 151 and 153 W. Mountain Ave.

Finding space for OtterBox’s 400 employees has been a struggle for the company, which got its start in a Fort Collins garage in 1998 manufacturing waterproof cases for PDAs. When the 52,000-square-foot headquarters opened in June 2011, it was at capacity with 250 employees.

Less than a year later, several of the building’s many conference rooms have been transformed into offices. Ancillary buildings, such as OtterBox’s facilities at 318 Canyon Ave. and on the second floor of 201 W. Mountain Ave., have taken on more overflow as the company continues to grow.

More employees could be squeezed into the existing space, Thomas said, but preserving the culture of the company is important to the executive team, a culture that includes lots of “space for creativity” for employees.

OtterBox’s staffing growth is a reflection of its revenue growth: OtterBox’s revenue grew by 106 percent from $170 million in 2010 to $350 million in 2011, according to Business Report research.

As the company continues to grow, the hope is to create an “innovation center” that fosters entrepreneurs and helps create even more high-quality jobs locally.