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.
Get the latest on the California Legislature's final hours of work for the 2013-14 session.
Releasing reservoir water to keep salmon from dying is one of many tough water allocation decisions in this third year of the California drought.
California's drought is blamed for a big downturn in honey production.
Researchers say California has been overdrawing its water account for a century.
Researchers at UC Davis fear that California’s drought may soon claim its first victim, the Red Hills Roach. The tiny fish is losing its water. Scientists fear it may soon be pushed to extinction.