The Didion Gustin Costello Group

Oconomowoc Office
Phone: (262) 567-9320
Toll Free: (800) 950-9320
Fax: (262) 567-3182
Email Us
1245 Corporate Center Drive
Oconomowoc, WI 53066
Our Networks

Our team is built upon shared values of honesty, integrity, genuine concern for clients, and respect for associates. These values drew us to join Baird and remain central to our ability to earn the quality client partnerships and maintain the high standards that are Baird traditions. Contact us today to explore a partnership with the Didion Gustin Costello Group and Baird.

Mark Gustin
Mark Gustin

Financial Advisor
Qualified Plan Financial Consultant
(800) 950-9320


Mark graduated from the University of Wyoming with a bachelor’s degree in elementary education. Before joining Baird, Mark served the needs of clients at Thrivent Financial after a career in teaching, coaching, and educational publishing. In describing the philosophy of the Didion Gustin Group, Mark says, “We work to remove the stresses of planning for your future. First we listen, then we work with you to build the retirement and legacy of your choosing.”

In addition to his experience working with private clients, Mark has earned the Qualified Plan Financial Consultant designation and has a focus on working with businesses to evaluate and build company retirement plans. This service helps companies to better meet the retirement needs of employees, partners and owners.

Mark and his family live in Fort Atkinson, where he has been involved in various outdoor support programs, a Hunter Safety Instructor, a co-leader in Cub Scouts, assistant little league coach, Make A Difference Wisconsin Volunteer Instructor, and FBLA volunteer. He was also a member of the 25th Fort Atkinson Area Chamber of Commerce Project LEAD. In his free time, Mark enjoys spending time with his wife Pam and three children, Gracie, Gabe, and Garrison, as well as camping, fishing, and fitness.

Nick Costello
Financial Advisor


Nick's mission is to be his clients' financial advocate, facilitating their unique goals, while adapting to an evolving landscape. Nick rejoined Baird in 2016 and brings over 16 years of industry experience with him to the Didion Gustin Costello Group. He believes a financial plan provides a foundation to implement a customized investment strategy to achieve the unique goals of his clients. His area of expertise includes a process-driven approach toward investment management.

Nick and his wife, Andrea, have lived in Milwaukee for 11 years with their two sons, Jayden and Luca. In his free time, Nick coaches his sons' sports teams and volunteers with St. Robert's school and the Bavarian Soccer Club.

Erin Nowakowski
Assistant Vice President and Office Administrative Manager





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