DARIEN — This hometown bank has made it to the big city.

Darien Rowayton Bank has signed a six-year lease at 855 Main St. in Bridgeport, across the street from the headquarters of People’s United Bank.

The nearly 12,000-square-foot space is owned by Main State Ventures, a joint venture of Forstone Capital, of Darien, and Norwalk-based Spinnaker Real Estate Partners. The 100,000-square-foot building has undergone extensive renovations to the lobby, common areas and parking garage, and recently completed an overhaul of its mechanical system and installation of new energy-efficient windows.

“The 855 Main St. location is an ideal move for our institution,” Bob Kettenmann, president of DRB, said in a statement. “We have been seeking an expansion location for months and with our specific requirements, Main State Ventures was able to hone in on the newly renovated space. Once we saw what was possible at the building, we knew downtown Bridgeport would be a perfect location for our expansion. Our entire team is delighted to join other top corporations in the downtown Bridgeport area.”

Darien Rowayton Bank has branches in Darien, the Rowayton section of Norwalk and the Southport section of Fairfield.

Marking its 10-year anniversary this year, DRB has built a deposit base totaling $522 million as of June 30, according to data on file with the Federal Deposit Insurance Corp.; the past few years, the company has expanded its lending base to student loans.

“We are thrilled to welcome Darien Rowayton Bank to 855 Main St.,” said Scott Raasch, director of business development for Forstone Capital. “A high quality tenant such as DRB is not only a great addition to our building, but to all of downtown Bridgeport.”

Peter Gioia, vice president and economist for The Connecticut Business & Industry Association, said the expansion is a testament to how successful the bank has become over 10 years.

“I think banks expand to grow business and the bank is obviously doing very well if they’re able to take on an expansion,” said Gioia. “Downtown Bridgeport is a commercial area, so I’m sure they’ll gain a lot of business there.”

Gioida also said the bank expansion is a reflection of the economy as a whole.

“The economy is expanding out of the recession. Jobs are being created and businesses are expanding,” Gioida said. “These businesses go to the banks for loans, which gives the banks more business as well.”