Eastern Bank of Boston and the Community Bank of Brockton said Friday that they plan to merge by year’s end.

Eastern Bank is a mutual bank, and the Community Bank is a cooperative bank, and no premium was paid, the two banks said.

In a statement, Community Bank president and chief executive John J. O’Connor III said that his bank, with five branches and $323.9 million in assets and $278.3 million in deposits, “needed a partner in order to meet the needs of our communities.”

Eastern Bank has 94 banking offices in Eastern Massachusetts, in addition to 22 Eastern Insurance offices. It has $8 billion in assets and $6.5 billion in deposits.

Eastern Bank chairman and chief executive Richard E. Holbrook said the merger will enable Eastern to better serve southeastern Massachusetts and Cape Cod.

Eastern Bank said that this is the fifth time in the past 30 years that Eastern has merged with another mutual organization in Massachusetts.

The merger needs regulators’ approval.