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.
Improved drought conditions and more renewables lead to decrease in natural gas use this summer.
Californians' water use kept creeping back up in July after the lifting of mandatory statewide conservation orders for the drought.
A new study shows fire-fighting foam containing highly fluorinated chemicals is contaminating drinking water supplies around many of the nation's military bases, airports and industrial sites.
It has been a busy fire season across California. But there are fewer fires in the state’s 18 U.S. national forests so far this year, compared to 2015.
Update 8:00 p.m. Sunday: Crews are making "good progress" on the Cold Fire in Yolo County, now at 60% containment. In Monterey County, the Soberanes Fire remains at 45% containment with wind creating an additional challenge for firefighters.