A pair of mergers later this year will see two of Massachusetts’ smaller credit unions combine into larger institutions.

Credit Union of the Berkshires, a Pittsfield-based institution with about $22 million in assets and 1,900 members, plans to merge into Greylock Federal Credit Union, the largest credit union based in Western Massachusetts with about $1.4 billion in assets.

The two Pittsfield credit unions have reached a definitive merger agreement and plan to combine in the late fall, Greylock Federal Credit Union said in a statement. The merger is subject to regulatory and CUB membership approval.

“We are pleased that Greylock and Credit Union of the Berkshires have reached this merger agreement,” Greylock President and CEO John Bissell said in the statement. “We know that the credit union difference remains strong in Berkshire County. We look forward to completing the merger and combining the resources of CUB and Greylock to help the community thrive.”

Greylock has about 90,000 members, and its field of membership includes those who live, work, attend school, worship or regularly conduct business in Berkshire County; the towns of Westfield, Southwick, Granville, Montgomery, and Russell, Massachusetts; Bennington County, Vermont; and Columbia County, New York.

“Credit Union of the Berkshires has taken great pride in serving our community and our membership for over 80 years,” CUB CEO Melissa Morin said in the statement. “We are confident our members will receive the highest quality of service they are accustomed to and deserve at Greylock. Greylock’s mission and core values align perfectly with Credit Union of the Berkshires and that’s why we have chosen Greylock as our merger partner.”

Also planning a merger are Worcester-based St. Vincent Hospital Credit Union, which has about  $15 million in assets and 1,500 members, and Shrewsbury-based Central One Federal Credit Union, which has about $685 million in assets.

In a document about the proposed merger on its website, St. Vincent Hospital Credit Union said the reason for the merger was “to enhance the services, benefits, and convenience to members of both credit unions and the communities we serve.”

“Partnering with another established credit union will significantly increase operating efficiencies so we will have the resources to deliver much more to SVHCU members along with the same personalized service we always provide,” SVHCU said.

The credit union added that the merger would also give members well-developed online and mobile technologies, new products and services, and highly competitive rates. The merger is expected to close in mid-July.

Central One Federal Credit Union recently expanded its membership, which now includes anyone who lives, works, worships, volunteers, attends school or owns a business in all of Worcester County and parts of Middlesex and Norfolk counties.

These mergers follow one early this year that saw Gloucester Municipal Credit Union combine with Metro Credit Union.