Following the onboarding process in-branch or online, RiverTrace follows up with additional emails to remind them of available products and services.

"We want to make sure we are hitting them with several different avenues of information to let them know there are other things we can do for them," she said. Those follow-up communications with new members has been effective in getting them to take out new products and services such as checking accounts, credit or debit cards, and new loans.

In addition, McDermott noted signing up younger borrowers through Google, Facebook and the credit union's blog helped cut costs by automating credit assessments with an online and mobile phone self-service account opening product integrated with RiverTrace's core system.

"We find that a lot of people are using [technology] not only to establish their checking accounts and savings accounts, but also loans because it does give them a preliminary approval based on the credit criteria that we have set up," McDermott said.

RiverTrace also hired WebStrategies to help with marketing on the internet and leveraging social media to drive business to the credit union. Through the use of SEM and SEO, this has helped the credit union retain members by communicating and transacting with them over the digital channels they use.

McDermott also noted RiverTrace has been very successful with sending promotional materials via email to existing members and/or the contact person at one of its SEGs.

The $1.2 billion Altura Credit Union in Riverside, Calif., increased its membership by about 28,000 in 2015 when it merged with the $342 million Visterra Credit Union in Moreno Valley, Calif. The consolidation placed Altura among California's top 40 largest credit unions by assets and members.

Since that merger and throughout this year so far, Altura said it is attracting about 1,200 new members per month on average.

Altura COO Jennifer Binkley said the credit union has been targeting younger and older millennials, including Generation Z (born in 1996 and later) and Latinos.

Among the 1,200 new members joining the credit union monthly, more than 551 are millennials in the 18 to 24 age group, which also includes some Generation Z members, and 25- to 34-year-old millennials. In addition, Altura is signing up about 200 new Latino members monthly.

Altura employee teams help develop the millennial products and marketing every year.

"They come up with the campaigns and what the giveaways are, and they do a lot of business development by going out to the local shopping centers, the local colleges and high school students who are graduating," Binkley said.

In 2008, Altura employees developed a simple checking product for 18- to 24-year-old millennials called iChecking with no monthly fees or minimum balances. iChecking also comes with a debit card that young members can personalize with a nickname or phrase. Altura also offers first-time auto loans to young millennials and Generation Z members who have little to no credit.

For older, 25- to 34-year-old millennials, Altura employees also developed the Nexus checking product that is free if the member has a loan or makes more than five debit transactions a month. The older millennials, Binkley noted, are always looking for ways to improve their credit profile so they can be prepared to secure a loan for that next big purchase.

"Their average balance is $332 and they use their debit card, on average, 33 times a month, compared to 19 times a month for our overall membership," Binkley said. "They are a good group to go after from a noninterest [revenue] perspective."

The $67.2 million Trius Federal Credit Union in Kearney, Neb., has also been successful in attracting young and older millennials, as well as young Gen Xers who are entering their 40s, as new members.

Trius saw its membership spike in early 2015 after completing a merger with the $14.4 million Kearney Eaton Employees Federal Credit Union and its 2,773 members. That consolidation increased Trius' membership ranks from 5,981 at the end of 2014 to 8,754 in early 2015 and the credit union ended up with 8,956 members at the end of the first quarter of 2015.

Throughout the second, third and fourth quarters of 2015, Trius grew its membership by more than 700, finishing the year with 9,690 members, according to its call reports. What's more, throughout this year, the credit union continued its organic membership growth and now serves 10,439 members.

Four years ago, Trius President/CEO Dee Schriner said the cooperative spotted an opportunity and decided to secure a community charter.

"There were more than 30 commercial banks in the community," Schriner said. "They were all competing for the commercial and agricultural loan business, but no one was focusing on the consumer loans, specifically out-of-the-box lending. Then we were granted a community charter four years ago to serve five counties, but we have hardly tapped that market because we are trying to manage our strategic growth."

Among the new Trius members, low-dollar loans are very popular.

"It takes just as much work as larger loans, but it is a product our members are needing," she explained. "They don't always need $5,000, so we are willing to do the $1,000 loan for them. My average loan is about $7,200."

Members use loans to buy a new washer and dryer, make major repairs to a car or for other unexpected, big-ticket expenses.

Trius' membership growth has certainly moved the needle on loans. In September 2014, Trius posted a total of 4,976 loans. By September 2016, the total number of loans increased to 7,986. Over the same two years, the credit union has seen strong spikes in payday alternative loans, new and used car loans and real estate loans.

To keep the membership growth momentum going, Trius has ramped up its advertising.

"We increased emails and other content marketing to members who, in turn, do a great job of spreading the word," Schriner explained. "Many new members say they chose us because of a recommendation by a friend or family member. We've done more community outreach and sponsorships to promote our new name, what we offer and what makes us different. Our unique market is saturated with financial institutions. We believe this environment allows us the opportunity to leverage the credit union difference."