The Ukiah Daily Journal reports that the county's Board of Supervisors on Tuesday voted unanimously to make the declaration, citing an "imminent threat of disaster" from drought conditions.
The state Department of Water Resources said Mendocino is the first to request state drought assistance.
Officials hope the declaration will result in state funds and assistance in developing a drought plan.
Gov. Jerry Brown has convened a task force to help decide if a statewide drought emergency is warranted.
State water managers say they will be able to deliver just 5 percent of the water sought by municipal agencies and nearly a million acres of farmland.
A winter forecast from NOAA's Climate Prediction Center Thursday shows the California drought may persist or intensify in parts of the state.
The Center for Biological Diversity filed notice of intent to sue the U.S. Fish and Wildlife Service Tuesday for not responding to a petition to protect 16 amphibian and reptile species in California
The Sacramento Region may get millions of dollars for water projects to help during the drought.
California has received less than 60 percent of the rain and snow this water year that it normally gets. Water managers are warning the new water year may be just as bad.
New motors, screens, and some casing repairs are in the works for eight of Sacramento's water wells. Some of the wells are more than 400-feet deep.