New Property and New Improvements to Property ORS 308.153

https://www.oregonlaws.org/ors/308.153

If an improvement to property, like a new structure,  appears on the overview map of the property but is not listed as a structure on the property nor has any permits related to its construction....

    then;

The property does not exist on the County Assessor Tax Roll.

If a structure is not on the County Assessor Tax Roll

   then:

It is not subject to taxation.

Rule:  All Structures and Improvements subject to taxation must appear on the County Assessor Tax Roll

Property Subject to Taxation
https://secure.sos.state.or.us/oard/displayDivisionRules.action?selectedDivision=421
(ii) Onsite developments (OSD) are land improvements within the site which support the buildings or other property uses. These include but are not limited to items such as grading, fill, drainage, wells, water supply systems, septic systems, utility connections, extension of utilities to any structure(s), retaining walls, landscaping, graveled driveway area. Onsite development is synonymous with onsite improvement.