In 1973, the Board of Supervisors received a request by petition from 22 Freestone property owners to establish a Historic District in Freestone, and to designate specific individual buildings as historic structures contributory to the Historic District, similar to the State of California historic preservation program. However, at the time a zoning classification for Historic District did not exist in the County Zoning Ordinance.
On April 23, 1974, the County established a program and administrative procedures for designating Historic Landmarks and Historic Districts through “Historic District” (HD) zoning under the Historic Zoning Ordinance (Ordinance No.1768). This ordinance also established the Sonoma County Landmarks Commission.
"Article XXVI(A). Historic Districts.
Section 26-192.1. Intent and Purpose. The Board of Supervisors finds and declares that the preservation of structures, sites, and areas of historical, architectural and aesthetic interest promotes the general welfare of the citizens of Sonoma County. The purpose if this district is to protect those structures, sites, and areas that are reminders of past eras, events and persons important in local, state, or national history, or which provide significant examples of architectural styles of the past, or which are unique and irreplaceable assets to the county and its communities, or which provide for this and further generations examples of the physical surroundings in which past generations lived, so that they may serve an educational and cultural function for the citizens of Sonoma County and for the general public."
In Sonoma County HD zoning is a "combining zoning district", meaning that it is a zoning classification applied in combination with the base zoning on a parcel. HD zoning does not change allowed land uses.
Sonoma County’s first survey of historic resources began in fall 1972, when the Planning Department began coordinating with geography faculty and students at Sonoma State College to conduct a Historic Resources Inventory. Work on the Inventory expanded during the 1974-1975 academic year to include geography and history faculty and students. The communities surveyed as part of the Historic Resources Inventory were:
- Glen Ellen and Kenwood
- Bodega, Bloomfield, Valley Ford, and Two Rock
- South Sonoma Valley
- Cloverdale, Geyserville, Alexander Valley, and Dry Creek Road in Healdsburg
Survey results were recorded on special forms that included the following for each property: a location map, a photograph, information on architectural and historical significance, a description of the condition of existing buildings, Assessor's Parcel Number (APN) and zoning, and owner name and address. About 500 properties were on this initial Historic Resources Inventory.
In January 1975, the County established the Historic Preservation Technical Advisory Committee, the major task of which was to review and elaborate on the raw data in the initial 1972-1975 Historic Resources Inventory, and identify areas suitable for preservation and future designation as Historic Structures or Historic Districts. The Technical Advisory Committee worked with representatives from these communities over several meetings to develop a list of historic structures and areas appropriate for preservation. The list was incomplete because many areas of the County had not been surveyed.
The Technical Advisory Committee published the "Historic Preservation Program: General Plan Technical Report" in 1976. It documented the County’s historic preservation activities to date, established the importance of design review in historic preservation, discussed how design review worked, and provided a list of historic sites and structures proposed for preservation.
Since that time, more than 3,000 additional surveys have been added to Sonoma County’s Historic Resource Inventory. The Historic Resources Inventory contains resources that have been designated as historically significant at the local, state or federal levels; as well as those that are potentially eligible.