Mercer Island, WA

Population: 23,256

see Mercer Island, WA on a map

Layman's version:
Can keep chickens in most residential zones as long as poultry housing conforms to setback and recommended space per chicken.

The Urban Chicken ordinance on the books:
Link to municipal code online: Mercer Island Code, Chapter 19.02 Residential

Text of municipal code:

19.02.010 Single-family

B. Additional Use Permitted in Zones R-9.6, R-12, and R-15. One accessory building for the housing of domestic animals and fowl, having a floor area not to exceed 36 square feet for each lot and located not less than 65 feet from any place of habitation other than the owners’; provided, the roaming area shall be fenced and located not less than 35 feet from any adjacent place of human habitation.