"We're mostly a credit union that operates through the mail," Mike Gardner, president/CEO of Good Samaritan, said. "We're open 24 hours a day with internet banking, but we don't have any branches, just the main office."

The credit union's sponsor is the Evangelical Lutheran Good Samaritan Society. With more than 240 locations across the country, the organization is the largest not-for-profit provider of senior care and other services in the United States, according to its website. More than 25,000 residents of all faiths live in retirement facilities operated by the society.

Chartered in 1973, Good Samaritan's FOM includes Good Samaritan employees, consultants, board of directors and their immediate families.

Whether it's a tiny cooperative with a handful of staffers, a mid-size credit union with a small crew that takes care of everything or a huge institution that contracts out some of its operations, achieving the right balance of full-time employees can be tricky.

New innovations such as interactive tellers, cloud computing, collaborative technology and unified communications have changed staffing needs and improved efficiency at many credit unions.

At the $1.4 billion Local Government Federal Credit Union, which ranked third on the CU Times' list for member-to-FTE ratio, 117 full-time employees serve nearly 250,000 members.

The Raleigh, N.C.-based cooperative is able to do so through a long-time partnership with the $29 billion State Employees' Credit Union, also based in Raleigh, according to Donna Gonyeau, Local Government's public relations manager.

Members of the credit union are served through SECU's network of 250 branches and more than 1,100 CashPoints ATMs across North Carolina, she said.

Partnering with the other credit unions enabled Local Government to reduce staffing needs, while allowing members to still have convenient access to accounts and services, Gonyeau said.

The alliance goes back to Local Government's creation, according to its website. At first, there was one credit union for all of North Carolina's government employees, both state and local, but some banks insisted the cooperative was serving more than its designated FOM.

To create a clearer delineation, Local Government was chartered in 1983 to focus on the local government employees and volunteers, while SECU continued to serve the needs of state employees. The model is still working great to this day, Gonyeau said.

Read more: One-person shop tops list …

The $26 million Garden State Federal Credit Union in Moorestown, N.J., which earned the top spot on CU Times' member-to-FTE list, is operated by only one employee, CEO Paul Ladd. 

He is also CEO of four credit unions and a privately-owned CUSO, Credit Union Services, all of which are headquartered in Moorestown.

In addition to overseeing the 3,800-member Garden City, Ladd is CEO of the $8.7 million, 1,840-member New Jersey Community Federal Credit Union, the $392,000, 140-member Camden Firemen's Credit Union and the $4.3 million, 600-member Acume, a federally-insured, state-chartered cooperative open only to employees of Moorestown Lockheed Martin.

Ladd's parents, John and Caroline Ladd, founded Credit Union Services in the mid-1960s, he said.

"It started as Ma Bell Credit Union in Camden, N.J., because my dad worked for Ma Bell," he said. "It kept expanding as other credit unions that were having trouble managing everything came to my parents for help."

Credit Union Services is a service center CUSO with about 10 employees that assist about 7,000 members in the four credit unions, said Ladd who has overseen the CUSO for more than three decades.

Over the years, he has shared his knowledge with other credit union leaders. For example, he spoke about his business model of managing day-to-day credit union operations, shared facility and shared staffing at a recent New Jersey Credit Union League workshop, according to the league's website.

Ladd said he values efficiency in all of the credit unions he manages.

"We try to keep things as automated as possible because otherwise, you're not going to make it happen," he said. "Automation is really the biggest key to efficiency."