This is the quote where I learned that a maximum of only ten animals is all that is permitted in Oregon:

"County laws can hinder or help animal hoarding interventions as found in a recent case Oregon. The laws governing animal ownership and care were vague, providing that citizens could own as many animals as they could reasonably care for. It did not allow law enforcement to enter a home without probable cause for a search warrant in order to check on the care and welfare of the animals. Once an extreme case of animal hoarding had been uncovered and it became clear how the law inhibited intervention and actually enable the animal hoarding to continue, and the law was immediately changed. Now it allows for up to ten pets to be housed without a license. If over ten pets are owned, the house is regarded as a shelter and is subject to regular inspection without a search warrant."
See the last paragraph here