Chicago-based Aon Hewitt, a large human resources firm, has acquired Modern Survey, a privately held, 40-employee firm in northeast Minneapolis that surveys employees for employers.

Terms were not disclosed.

Aon Hewitt said the addition of Modern Survey will strengthen its “suite of workforce analytics solutions, including … human capital analytics, employee engagement … exit surveys and 360-degree feedback.”

Don MacPherson and Patrick Riley founded Modern Survey in 1999. They previously were employees at Ameriprise Financial, working on employee-satisfaction surveys. The two were joined by Riley’s brother Dan Riley, who leads technology operations at Modern Survey. All three have signed contracts to remain with the organization for at least two years.

MacPherson, 47, said it was time to sell to a larger, stronger firm with a bigger footprint. Aon Hewitt will integrate Modern Survey’s technology and employee-measuring tools into its employee recruitment and HR consulting operations.

Modern Survey’s growth was “bootstrapped” out of owner’s equity and cash flow. MacPherson said it increasingly was challenged in the growing worker-feedback field by well-financed young firms backed by venture capital money, as well as competitors such as Towers Watson, IBM and Gallup.

“Even though we grew 40 percent last year [to revenue of $6 million-plus], our growth was starting to be impeded,” said MacPherson. “We felt that if we didn’t get growth funding, we were going to be just consumed. We started talking to Aon last May and we liked their leadership. Either way, we were going to give up control.

“They have a global footprint and that gives our staff incredible opportunities.”

Aon Hewitt is a U.S. subsidiary of Britain’s Aon PLC, a global risk management and insurance brokerage.