Plante Moran expands into Boston with acquisition of Tonneson + Co

Plante Moran, a Southfield, MI-based accounting and consulting firm, has acquired Tonneson + Co, a Boston-based accounting consulting firm.

The deal, which goes into effect on July 1, will expand Plante Moran’s physical presence into Boston and the state of Massachusetts.

Plante Moran is the largest accounting and consulting firm in Michigan, with approximately half of its nearly 4,000 employees based in the state. The firm also has offices in Colorado, Illinois, New York, and Ohio, as well as international locations in Mexico, India, China, and Japan.

“This partnership allows our combined firms to further enhance the capabilities we offer both clients and staff while preserving the unique culture and relationships that have defined Tonneson and Plante Moran for decades,” said Rick Mastrocola, CEO of Tonneson.

Tonneson was founded in 1975 and is one of the 25 largest accountancies in Boston. The firm has 100+ professionals providing audit, tax, and consulting services to clients across industries. Tonneson’s consulting offerings include M&A, dispute resolution, and succession planning.

“For 100 years, Plante Moran has prioritized long-term stability and client success, which has fueled the firm’s steady growth,” said Jason Drake, managing partner of Plante Moran. “Tonneson’s shared values and vision for the future make them an ideal partner. We’re excited to welcome their talented team and expand our presence in Boston.”

Plante Moran was founded in 1924 and is the 15th-largest accounting firm in the US, according to IPA, with $1.1 billion in annual revenue.