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.
The weather forecast through the weekend includes thunderstorms and lightning for parts of northern California, which could spark new wildfires.
Data released Thursday by the State Water Resources Control Board shows 265 out of 411 local agencies hit or nearly reached savings targets.
Triple digit heat has many people staying cool inside. But outdoor workers don't have that option.
The above-average rains of the past week did not ease drought conditions or improve reservoir storage in California. The drought expanded in other parts of the western U.S.
(AP) -- Democratic Sen. Dianne Feinstein of California has come out with a new drought relief bill that emphasizes long-term investments in desalination, recycling and new or expanded reservoirs.