Filling the gap between its South Coast and Cape Cod locations, First Citizens’ Federal Credit Union will open a branch office in Wareham next month.

The Fairhaven-based credit union announced that it will expand into the 396 Onset Ave. building previously occupied by Mayflower Bank.

“Wareham has always been on my mind,” President and CEO Peter Muise said in talking about the credit union’s plans late last week. “Wareham is a geographically large location and is very diverse. To serve the population and summer population is positive for us.”

Muise noted that Wareham is home to many small businesses, which he described as the credit union’s “niche.”

He also credited Wareham Community and Economic Development Director Salvador Pina for attracting him to the town. “Every conversation I’ve had with Sal has done nothing but whet my appetite further to branch out to Wareham,” he said.

First Citizens' traces its roots to Bristol Credit Union, founded in 1937 to serve employees and residents of Bristol County. Over the years, that charter has been expanded to include Plymouth, Barnstable, Dukes, Nantucket and Norfolk counties.

Like all credit unions, First Citizens’ is a non-profit organization, owned by its depositors, known as members.

Today, First Citizens’ is a $580 million-plus institution with 80,000 members, employing more than 180 people, with branches stretching from New Bedford to Taunton and out to Orleans.

But until now, the institution had no physical presence between its Mattapoisett and Cape Cod branches.

“When this opportunity came up, having an existing site that people knew, it’s a great opportunity for a business,” Muise said. “This being our first office in Wareham, we have recognition with this institution – the old Mayflower building”

The building became available after Mayflower Bank was acquired by Rockland Trust last May and consolidated the two institutions’ Wareham operations last fall.

Despite the loss of Mayflower, Wareham is becoming something of a banking hot spot. First Citizens’ will be joining a host of longer-established Wareham banking operations, including fellow credit union Plymouth County Teach Federal Credit Union. And Cape Cod Five Cents Savings Bank’s first full-service off-Cape branch bank is under construction at Rosebrook Place on Route 28.

Muise stressed that the new First Citizens’ branch will be car-friendly.

“Vehicle is the way to go,” he said. “You can make your visit to the bank within your daily commute. You can stop by when you’re dropping the kids off at school, going to the doctor’s office or the pharmacy.”

Vice President of Retail and Marketing Frank Almeida said that, if Mayflower Bank customers liked banking there, they will “love” First Citizens’ Federal Credit Union.

“We will take that and raise the bar,” Almeida said.