The deal announced Monday is subject to approvals from banking regulators as well as shareholders.
People's United Bank, based in Bridgeport and founded in 1842, has 413 locations in Connecticut, New York, Massachusetts, Vermont, New Hampshire and Maine.
United Bank, with corporate headquarters in Hartford, has 59 branches in Connecticut and Massachusetts.
People's United Chief Financial Officer David Rosato says the acquisition will result in cost savings, although there was no word on job losses or branch closures. In many communities, the banks have branches within two miles of each other.
Last fall, People's United completed its purchase of Farmington Bank for $544 million.
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