The site offers tips and resources related to sustainability, green building and conserving energy, among other topics, county officials said.
The Web site is aimed at helping public agencies, companies and individuals.
"The new Green Portal is an ambitious state-of-the-art method to provide the community with updates on what the county is doing to be more green and provide ideas on how individuals can lower their carbon footprint," Supervisor Rich Gordon, who chairs the Environmental Quality Committee, said in a statement.
In addition to launching the Web site, the Board of Supervisors has also signed a "Cool Counties" declaration, a pledge that requires the county to reduce carbon emissions by 80 percent from their current levels by 2050, county officials said.
The Web site can be accessed at www.co.sanmateo.ca.us/green.