A New Hampshire-based tax accounting firm will join Portland’s Baker Newman Noyes, creating the largest tax practice in northern New England.

William Steele & Associates PC and its 16 employees will join the firm Jan.1, bringing the total employee count at Baker Newman Noyes to more than 200.

“This move adds experienced colleagues to our highly regarded and thriving tax practice, providing our clients with even greater access to talent and resources. All around, this is an exciting next step in our growth plan,” said Ellie Baker, managing principal at Baker Newman Noyes, in a news release.

The 30-year-old William Steele & Associates is expected to boost Baker Newman Noyes’ revenue by 15 percent, bringing clients from throughout New England, as well as New York, New Jersey, California and Florida. It also serves international clients in Canada, Japan and other regions.

Once the merger is complete, employees of WSA will relocate to the downtown Manchester, New Hampshire, office of Baker Newman Noyes at 650 Elm St. The deal makes Baker Newman Noyes the largest tax practice in northern New England in terms of employees and revenue, according to company Chief Operating Officer Sean Sinclair.

WSA founder William G. Steele Jr. will become a tax principal of Baker Newman Noyes along with current partner Thomas W. Musgrave.

In mid-October, Baker Newman Noyes hired 13 people, continuing an expansion that ramped up in 2010 when it opened an office in Boston. The 20-year-old firm focuses on serving closely held businesses, public companies and high-net worth individuals and families.