Edit: I just poked around some more, and it looks like it changes since we were looking into it in 2014. Here is the new info-
https://www.sterlingcodifiers.com/codebook/index.php?book_id=998
It says- 5-4-5: LIVESTOCK AND FOWL PROHIBITED; EXCEPTIONS
C. Domestic Hen Chickens: Notwithstanding the foregoing, the keeping of not more than eight (8) domestic hen chickens is permitted in the rear yard of any single-family dwelling or duplex located in a residential zone, provided the following requirements are observed:
1. Eggs provided by such hens will not be sold for pecuniary gain or profit.
2. For the purposes for this subsection, the term "rear yard" means a residential yard lying between the rear lot line and the nearest foundation line of the main building and extending across the full width of the lot. In the case of a corner lot, where the building fronts on a side street, the rear yard may be established from the rear of the house to the side of the property line.
-so you can have 8 hens? I think.
My understanding is that if you are in city limits, yes it is prohibited. If you are not in city limits you are under county law which does allow them. My family lives in the general area and when we were thinking of looking for property there we ran into this issue.
For anyone who wants to look at it here is a link to the ordinances I found-
http://www.cityofrigby.com/use_images/citycode/citycode_animal_control.pdf
It is on page 4