810 Quincy Street | Rapid City, SD 57701
(605) 342-5630
(605) 342-2172

About Us

Ketel Thorstenson, LLP (KTLLP) has been operating as an accounting practice in Rapid City in one form or another since 1936, when Harold Heims first opened the practice and hired A.C. (Bud) Thorstenson shortly after. The firm started in offices above the old North Western Warehouse, and then moved to space above Staple & Spice. The building at the current 810 Quincy Street address was constructed in 1966; the same year that Roy Ketel and Rich Siekman worked together to form a new partnership.

The rich history of change and growth has led to three name changes and seven building remodels/additions. In addition to growing the practice, the Partners of KTLLP continue to be visionaries and delve into business solutions for their clients outside of traditional accounting services.

Today the KTLLP family employs over 120 professional staff members, including 18 partners, and operates out of Rapid City, Spearfish, and Custer, SD, and Gillette, WY. We are proud of our longevity and thankful for all of the clients who we consider as friends. KTLLP looks forward to many more years of continued growth serving the regional market.


  • To provide the finest professional services, including auditing, attestation, accounting, tax and consulting services.

  • To be associated with the region’s fastest growing companies and to help each client attain their maximum potential.

  • To be a firm that is an enjoyable and rewarding place to work and do business.

  • To contribute to our community and the profession to which we belong.

  • To grow, but never lose the local identity and personal relationship with clients that are the foundation of our practice.


Ketel Thorstenson, LLP subscribes to the Fish Philosophy which is framed by the following principles:

  • Choose your Attitude- We have a choice in how we decide to approach the day, our work and our clients. By choosing a positive and cheerful attitude we know positive things will happen.

  • Be Playful- Work and play can coexist. Play is a state of mind, it’s the light hearted feeling you release inside people when they are enthused, committed    and free to laugh.

  • Make Their Day- It encourages us to focus on our customers and how we can help them. It pushes us to get to know our customers and figure out what they want/need so that they return to us for continued service.

  • Be Present- We focus on the here and now, not the past or future, so we can be fully engaged with our customers and  on our work.

Large star stylized

Made a complex scary issue informative and achievable.

Service Business,

Thank you for providing another great learning opportunity. I’m glad I came.  I’m down in the weeds and it’s good to step back and get the big picture.

Carolyn Ness
Associate Director, Northern Plains Eye Foundation



810 Quincy Street
Rapid City, SD 57701

(605) 342-5630

(605) 342-2172


123 E. Jackson Blvd.
Suite 2
Spearfish, SD 57783

(605) 642-7676

(605) 642-2616


609 Mt. Rushmore Rd.
Custer, SD 57730

(605) 673-3220

(605) 673-3114