William Niemi is a supporter of many community organizations in the Sacramento region as well as state and national associations that support housing.
- Founding President of HomeAid of Sacramento
- Member Rotary Club of Sacramento
- Supporter of restoration of the historic Cathedral of the Blessed Sacrament in Sacramento
- Supporter of the California Homebuilding Foundation
- Supporter of the Los Rios Community College District Foundation
- Supporter of Homes for America Alliance
- Supporter Fix Housing First
- Donor CalCPA Institute