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 San Joaquin County Board of Supervisors has voted to continue its drought emergency while other counties are looking at lifting conservation measures.
A UC Santa Cruz study finds transmission of West Nile virus is higher in drought years.
Today's Sierra snowpack survey has scientists with the California Department of Water Resources optimistic about the state's water supply.
California farms and ranches saw a nearly 17 percent drop in revenue from 2014 to 2015, according to a new review. The decrease had little to do with the drought.
California's tree die off has led a state oversight board to review forest management policies.