The Oak Brook office was established after Crowe combined practices with the public accounting firm Hartley, McKenna, and Flood in 1986. In 2005, the Oak Brook office grew by adding PTW, a government and not-for-profit consulting and accounting firm. Since then, the office has continued to grow through expansion of services and industry expertise. Today, more than 300 personnel are aligned to the Oak Brook office and provide service to a diverse client base, including Fortune 500 companies and state agencies, as well as some of the largest manufacturing and financial services companies in Illinois.