ERA Key Realty Services, whose Milford headquarters are pictured above, has merged with Century 21 Millennium in Westborough. ERA is one of the largest real estate firms in Worcester County.

ERA Key Realty Services, one of Worcester County’s largest real estate firms, has merged with Century 21 Millennium in Westborough.

The Westborough office, located at 18 Lyman St., is the second new office for ERA Key Realty Services in just over a month. The firm opened its Worcester office at 29 East Mountain St. in late August. In early July, the Milford-based company announced a major expansion into the city of Worcester, after hiring more than two-dozen new agents earlier in the year.

“We’ve grown around the city of Worcester with offices in Whitinsville, Oxford and Spencer,” said ERA Key President Bruce A. Taylor at the time. “Rather than expanding around the city we decided to take the bolder step of moving into the city.” The company also has offices in Framingham and Hopkinton.

The firm has hired 28 new agents since the beginning of the year, and the recently opened Worcester office has the capacity to add 50 more agents to the firm’s payroll. ERA Key is the fifth largest agency out of more than 2,600 in the ERA franchise network and the second largest independently owned ERA agency in the nation.

The Westborough office was purchased from Edward Henderson, who also operates Century 21 Millennium-Henderson in Upton. Henderson will continue to operate the Upton office and will maintain a financial interest in the Westborough office, but ERA Key will manage the office, according to a press release issued last week by ERA Key.

The 1,600-square-foot office can accommodate 18 agents but an additional 800 square feet is available next door, which would provide space for a total of 25 agents. The office currently has nine agents, including two who transferred from other ERA Key offices.