In 1935, Charles K. Willett founded C.K. Willett, Consulting Engineers with three employees.   The office was located at the corner of First Street and Ottawa Avenue in Dixon, IL.  As the company grew he moved to offices in the City National Bank building, and then to 317 N. Galena Avenue, Dixon.   In 1962 C.K. Willett purchased the former office building of the Reynolds Wire Division of the National Standard Company, and he moved the entire operations of the firm to the new building in July of 1962.

In 1966, C.K. Willett, Consulting Engineers merged with Robert Hofmann & Associates to form Willett, Hofmann & Associates, Inc., and the firm grew to four offices in Dixon, Rockford, Sterling, and Joliet, IL.

In October of 2005 Gastel & Associates, P.C. merged with Willett, Hofmann & Associates.  Gastel & Associates, founded in 1970, had been Freeport's oldest land surveying and engineering firm, providing civil engineering, agricultural engineering and land surveying in Freeport and the surrounding area for over 35 years.  The merger created a combined force of unmatched expertise for the region. 

Today Willett, Hofmann & Associates has a staff of over 50 professional engineers, structural engineers, professional land surveyors, architects, technicians and support staff working out of offices in Dixon, Rockford, Freeport, Sterling, and Joliet, Illinois and Monroe, Wisconsin.