Voters in San Benito and Mendocino counties adopted the ban Tuesday.
Fracking is a method of forcing chemicals and liquids underground to extract deposits from aging oil and gas fields. None of the three counties are known to currently have fracking operations.
California is the country's third-largest oil producer. Other places in the state and country also have enacted fracking bans.
Chevron, ExxonMobil and other oil companies donated about $7 million to try to defeat the fracking bans in the three coastal counties.
Supporters of the fracking bans argued that contamination of water supplies from fracking is inevitable. Opponents of the bans warned of lost jobs in the energy industry and potential lawsuits over a ban.