Newport Beach-based Alliant Insurance Services acquired on undisclosed terms Mesirow Insurance Services, a division of Mesirow Financial in Chicago.

The division will join Alliant Americas, the firm’s middle-market insurance group, and gives it entree to the Midwest insurance market.

“This partnership will create a center of excellence for insurance, employee benefits, and risk management throughout the Midwest,” said Alliant Chairman and Chief Executive Tom Corbett.

MIS will keep its business name, continue with a base in Chicago, and retain its leadership and 350 employees. It also will continue to operate satellite offices elsewhere in Illinois and in Denver, Colo.

Mesirow Financial will receive an equity stake in Alliant as part of the deal, the Chicago Tribune reported.

MIS offers property and casualty insurance, employee benefits, life and disability, private client insurance, and structured settlements. Its parent company, Mesirow Financial, is an 80-year-old independent, employee-owned financial services firm.

Alliant Insurance Services is one of the largest insurance brokerage firms in the U.S. and provides insurance products and services to more than 26,000 clients. It reported $829 million in revenue last year and employs 201 locally and almost 2,200 companywide. Employees own about 40% of the firm. Another 43% is owned by private equity firms KKR in New York and Stone Point Capital in Greenwich, Conn.