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 movement around the U.S. encourages people to skip the shopping malls Friday and spend time in nature. Some national parks and state parks in California are waiving entry fees.
The latest U.S. Drought Monitor showed no change to drought conditions in California over the past week. But, the report does not include the storm that brought rain to valleys and snow to the Sierra Nevada this week.
Two million Sacramento-area water users conserved 27 percent in October, the same rate as September.
A California law, which was passed to respond to the drought- allows artificial turf on all residential property. But a Sacramento city councilman says the law should allow cities to restrict its use.
There is no change this week to the drought in California, despite the recent storms that have brought snow to the Sierra. Reservoir storage in California remains the second lowest on record.