[2] In 1964, the company was built by William Stookey and Dan Heil in southern California on a then-unique model of providing outsourced engineering services exclusively to municipalities, especially newly urbanizing cities.

[7] Willdan acquired NYC-based Genesys Engineering, P.C., in 2016, bringing Power Engineering services into its portfolio, with an eye to evolution of U.S. power systems toward Distributed generation and microgrids.

IA's software solutions help investor-owned utility and smart city managers solve problems arising from the transformation of an electrical grid facing growth in distributed generation sources, such as solar power and the electric vehicle, effectively harnessing the power of renewable energy and energy storage.

[9] The energy engineering and sustainability firm of Newcomb Anderson McCormick, Inc. was acquired by Willdan in April 2018, bringing strong relationships as a long-term energy efficiency, renewable energy, and green buildings consultant for the University of California, California State University, and California Community Colleges System, and with San Francisco Bay Area public agencies and utilities.

[12] In July 2019, Willdan entered a $200 million expanded credit facility to fund future acquisitions, and also announced its acquisition of Onsite Energy Corporation, adding industrial sector clients for Willdan's energy efficiency services.