Every City and County has their own rules.  Counties have health department rules AND building, fire and public safety rules.

Environmental Health Department Rules are here

Mobile Food Unit Guide

Public Works & Planning Department

Contacts:

Planning Division
5155 Silverton Rd. NE
Salem OR 97305
Ph. (503) 588-5038; fax (503) 589-3284
http://www.co.marion.or.us/PW/Planning

Mobile Food Vendor Permit

Use Standard for Mobile  Food Units 16.26.570