mother ducker,
Are you in cook county? If so, then they are ilegal. I've read through the vast majority of the municiple codes for cook county. The code about animals pretty much says:
(17) To have more than three adult companion animals living at any one individual residential unit. The term companion animal shall include domestic dogs, domestic cats, and ferrets. For purposes of this article, an animal shall be considered an adult when it reaches four months of age.
They consider all poultry to be Vectors. A vector is an animal capable of carrying disease producing organisms to a human host.
Pretty much, ducks/chickens are not allowed in residential homes/properties because they can "spread" disease. They are allowed on farms (obviously) which believe have some commercial aspect to them.
It's really long and annoying, and i checked in with a friend of mine who is a cook country cop. If you are in cook county, be very warry!