It's illegal on my town to have chickens on anything less than 5 acres. I have an acre that backs up to woods far enough away that a couple hens would be no problem, but nope. One of my neighbors has 4.6 acres and used to have chickens but had to get rid of them when they changed the law. Its extra sad that my house is an original 1900s farm house with the original barn that used to have donkeys, chickens, goats and a few cows sitting on 20 acres, now I'll get fined to oblivion if I so much as get 1 quail.

USA

I don't think it's exactly against the law. Though the local HOA might have something to say about it.

But noise complaints are noise complaints, whether or not you like the sound of chickens if they're being too loud you're going to get a knock on the door. Same as if you had a very annoying dog.

My guess is "places that have lots of predators and don't want them being attracted to residential areas". I can see an argument for banning chickens in a suburb if, say, little Susie down the street got attacked by a hungry coyote that couldn't make it into any of the coops (i have no clue if coyotes would attack a kid or not, just an example).