Generally, credit unions with less than $50 million in assets merge into larger credit unions to offer their members additional services such as mobile banking, which many small credit unions cannot afford to provide on their own. Other small credit unions have blamed their decision to merge because of increasing costs of regulatory burdens, operations and low interest rates.

Though it's difficult to predict how the credit union merger landscape will develop over the next five years, Worth said he doesn't see anything that will change the fundamental merger trends that have occurred over the last five years.

One thing is for sure, however, is if the current trend line holds to about 229 mergers a year, there will be 5,409 credit unions by 2018 and 4,264 credit unions by 2023. Currently, there are 6,554 credit unions, down from 7,699 cooperatives in 2009, according to NCUA.

Most of the mergers have occurred in 10 large-population states that have more than 200 credit unions, except for Virginia and Wisconsin, which have 166 and 174 credit unions, respectively, according to NCUA data.

Last year, California posted the most mergers (18), followed by Illinois (17), New York (17), Ohio (15), Pennsylvania (15), Wisconsin (15), Texas (12), Michigan (12), Virginia (11) and Massachusetts (10).

These states accounted for 142, or nearly 60%, of the 243 credit union mergers in 2013.

Typically, Worth said, large states post the most mergers because they have a high number of credit unions, including more credit unions with assets of less than $50 million.

For example, California had 81 mergers over the last five years, or about 16 consolidations a year, but still has 369 credit unions. Pennsylvania posted 77 mergers over the last five years, or about 15 every year, but still has 487 credit unions.

Nevertheless, in some of the other high population states with more than 150 credit unions, only a few mergers occurred annually.

For example, in Florida with 158 credit unions, there were 25 mergers over the last five years, or about five a year on average. Last year, the Sunshine State posted only three mergers.

In New Jersey where there are 196 credit unions, only 23 mergers occurred in the Garden State from 2009 to 2013, or an average of 4 per year. New Jersey did post six consolidations last year, according to NCUA.

Additionally, in Tennessee with 160 credit unions, there were 29 mergers from over the last five years, or about 6 mergers a year. The Volunteer State recorded eight consolidations last year. And in Indiana with 158 credit unions there were 29 mergers over the last five years or about six annually. The Hoosier State posted six mergers in 2013.

“Obviously there are many factors driving merger decisions,” Worth said. “One driver in the data is simply that as there are fewer credit unions in a state (i.e., Florida, New Jersey, Tennessee, Indiana) the proportion of very small credit unions is generally smaller — thus there are relatively fewer merger opportunities or targets.”

Seven states — Alaska, Maryland, Maine, Montana, Nebraska, Nevada and Wyoming — posted no mergers last year, according to NCUA. All of these states have fewer than 100 credit unions each.

Another seven states with fewer than 100 credit unions, Arkansas, Arizona, Mississippi, New Hampshire, New Mexico, Rhode Island and Vermont, each recorded only one consolidation last year. However, some states with more than 100 credit unions, such as Georgia (138,) Missouri (130) and Washington (106), only posted one merger in 2013.