The Clinic was incorporated under Wisconsin law in 1916 and operates as a charitable corporation with all of its assets held in a charitable trust. It is one of only a few large independent nonprofit medical clinics in the United States

Marshfield Clinic is the largest private group medical practice in Wisconsin and one of the largest in the United States, with more than 700 physicians representing over 80 different medical specialties, more than 6,000 additional employees, and over 50 locations in northern, central and western Wisconsin.

The Clinic had nearly 3.8 million patient encounters for the year ended September 30, 2011, and reported 383,380 unique patients in the Clinic system during this same period.