According to the Ventura County Tax Collector's website (http://www.ventura.org/ttc):
You may be obligated to acquire a Ventura County business license and pay a Transient Occupancy Tax (TOT) to the County of Ventura if you rent out a residential property for periods of 30 days or less in the areas of Ventura County that are outside any city limits. Often described as short-term vacation rentals, and often listed on websites like Airbnb.com (among several others), these rentals are subject to Ventura County's Uniform Transient Occupancy Tax Ordinance (Division 11, Chapters 1-3, Sections 11111-113212). The ordinance does not apply to owners who continuously reside on the property while renting out rooms. For further information, contact the Treasurer-Tax Collector at 654-3775.