About Us

Small Business CPA Services PhotoIn 1964, Dan Gardiner started providing CPA services for the co-op and agribusiness industries. Over the years, as his expertise and client list grew, the company became Gardiner & Co. P.C. In 2003, as sons Daniel (Mark) and Dennis were made partners, the name was changed to Gardiner Thomsen P.C., to also include the name of long-time colleague and partner, Dave Thomsen.

Over the last 45+ years, we’ve grown to be one of the most respected CPA firms in the Midwest. We specialize in accounting and business advisory services for co-ops, agribusiness, credit unions, government agencies and closely held businesses, and have added offices in Iowa, South Dakota and Nebraska. Our growth and success is evidence of our dedication to being trusted business advisors to our clients.


We’ve asked our clients about their reasons for working with us, and overwhelmingly, they say it’s because of our employees. Every day, in every client interaction, our employees deliver the quality reputation we’ve built at Gardiner Thomsen. We’re proud of our Mid-western roots and the fact that we like to roll up our sleeves and get to work. We do business differently – we’re passionate about our clients and their specific industries, and we consider ourselves to be a part of their team.

Click here to meet our staff:  Des Moines Office, Charles City Office, Lincoln Office, Sioux Falls Office.


We earn our clients’ trust by being consistently dependable. That’s why many of our client relationships date back more than 40 years in cooperatives, 25 years in credit unions and 20 years in governmental entities. During that time we’ve seen just about every best practice, every problem, and every solution. Having that experience, and putting into practice, enables us to pass on that knowledge so our clients can be more efficient and profitable.