Postmile System

The Postmile Book

The Sonoma County Postmile Book is a comprehensive listing of significant locations along County-maintained roads (e.g. intersections, bridges, city limits, etc.)

View/Download the Sonoma County Postmile Book (PDF)

Total Road Miles

The County-Maintained Road System currently includes 1,368.77 centerline miles of roadway. Centerline mile totals account for the total road length, not accounting for roadway width or number of lanes.

By Supervisorial District

District 1District 2 District 3 District 4 District 5 

By Functional Class

Principal Arterial Minor Arterial Major Collector Minor Collector Local 

Last updated July, 2017

What is a postmile?

A postmile (AKA post mile) is a numerical value that identifies a specific linear location along a County road, based on its distance (in miles) from the beginning of the road (e.g. if you are at postmile 10.00, then postmile 11.00 is one mile up the road). All Sonoma County roads have designated beginning and ending post mile assignments.

Contact Information

Business Hours
Monday – Friday
8:00 AM – 5:00 PM
Contact us by Phone
Office Location
La Plaza B
2300 County Center Drive
Suite B 100
Santa Rosa, CA 95403
38.462023, -122.725381

Interactive Maps

Sonoma County Interactive Maps


Thematic interactive maps for Sonoma County