For more than 50 years, Gardiner Thomsen has proven itself as a trusted partner for its clients across the country. We specialize in accounting and business advisory services for agribusiness, cooperatives, credit unions, government agencies and closely held businesses. Our offices in Iowa, South Dakota and Nebraska are known industry-wide for their dedication, steady dependability and experience and are the pillars in which our growth and success is founded.

The same sort of integrity and honesty that inspired Dan Gardiner to provide common sense CPA services to his clients in 1964 inspires us today, through Dan’s two sons, Mark and Dennis, and the entire Gardiner Thomsen team, which works hard every day because so do our clients, and they deserve the same.

Meet our staff


When we ask our clients why they work with us, they overwhelmingly say it’s because of the people at Gardiner Thomsen. Every day, in every client interaction, our employees deliver the quality reputation we’ve built here. We’re proud of our Midwestern roots and of the fact that we like to roll up our sleeves and get to work. When you work with Gardiner Thomsen, you are getting the knowledge and capabilities of world-class CPA services, but you are also getting a support system that is invested in your success. You are getting a partner and we passionately consider ourselves to be part of your team.


In 1964, Dan Gardiner started providing CPA services for the agribusiness and cooperative industries. As his experience and client list grew, the company became Gardiner & Co. P.C. In 2003, as sons Mark and Dennis were made partners, the name was changed to Gardiner Thomsen P.C., to include the name of Dan’s long-time colleague and partner, Dave Thomsen.

Today, Gardiner Thomsen operates very much like it did when Dan founded it–through hard work, integrity and common sense. We’ve grown exponentially and we remain on the cutting edge of accounting services but we still believe in making partnerships with clients, in handshakes and cooperation, in associations that are mutually beneficial. For more than 50 years, those have been our driving principles and they’ll keep driving us for the next 50.

“...I have had several inquiries about Gardiner Thomsen from other cooperatives or cooperative-related entities. I never hesitate to put in a good word and/or reference. Not to be nice…to be factual and to tout a good company.”

Doug Ohlson, General Manager, Frenchman Valley Coop (FVC)