Read this as a map, not as advice
This page points at the rules that apply to breeding and selling dogs in Illinois, and links the text of each one so you can read it yourself. It is not legal advice. Nobody here is a lawyer, and a real situation can turn on facts a web page cannot know.
Local rules sit on top of state ones. A municipality can require things the state does not, and a lease or a condominium association can restrict what both of them allow.
The line that decides whether you need a state license
The Animal Welfare Act defines a dog breeder as a person who sells, offers to sell, exchanges, or offers for adoption dogs they have produced and raised. Then it draws the line that decides most cases: a person who owns, has possession of, or harbors five or fewer females capable of reproduction is not a dog breeder under the Act.
One litter from one or two dogs does not make you a licensed breeder. At six intact females you are one, and Section 3 requires a license from the Illinois Department of Agriculture before operating as one.
Watch the vocabulary. The Act defines "offer for sale" to include advertising, bartering, auctioning and giving an animal away, so a free puppy is still an offer for sale in the language of the statute.
Eight weeks, at the earliest
Section 2.2 says no dog dealer, dog breeder or cat breeder shall separate a puppy from its mother, for the purpose of sale, until the puppy has reached eight weeks of age.
Those are defined terms, so an owner below the licensing line is not who that sentence is aimed at. Hold to eight weeks anyway. What a puppy learns from its mother and its littermates in those weeks is not available from anywhere else, and the veterinary behaviour literature treats this period as the one that shapes how a dog copes with everything after it.
What the state expects to change hands at a sale
Section 3.1 lists what a licensed dog breeder or dealer must provide for every dog offered for sale: age, sex and weight; breed; a record of vaccinations and veterinary care; whether the dog has been sterilised; the name and address of the breeder; the name and address of anyone else who owned or harboured the dog before the sale; and documentation that the dog is microchipped and enrolled in a nationally searchable database.
Below the licensing line that list does not bind you. Hand it over anyway. It is the state’s own answer to what a buyer deserves to be told, and it is the cheapest credibility available to you.
Rabies is not optional
The Animal Control Act requires every owner of a dog four months or older to have it inoculated against rabies by a licensed veterinarian, with a second vaccination within one year of the first, and later boosters governed by the licensed duration of the vaccine used.
Your veterinarian files the certificate with the county, and that certificate carries the dog’s microchip number if it has one. Keep your copy somewhere you can find it. City registration, boarding kennels and grooming appointments all ask for the same page.
If you are in Chicago
Chicago requires a city dog license for every dog four months or older, under Municipal Code 7-12-140, and will not issue one without proof of current rabies vaccination.
The fee is set by ordinance and is far lower for a sterilised dog. At the time of writing it is five dollars a year for a sterilised dog against fifty for an unsterilised one, with a reduced rate for senior citizens. The City Clerk issues the licence, online or in person, and publishes the current fees.
Outside the city, check your own municipality. Registration, limits on the number of dogs in a household and kennel rules are all set locally, and they differ from one suburb to the next.
The rules people quote that do not cover you
Two well known parts of the Act are aimed at shops. Section 3.8 allows a pet shop to offer a dog only if it came from a shelter or an animal control facility, and Section 3.15 sets out what a pet shop must disclose before a sale, along with the remedies a buyer gets when it does not.
A person who sells only animals they produced and raised is excluded from the definition of a pet shop operator, so none of those buyer protections attach to a private sale. Nothing fills that gap except the agreement the two of you write, which is the next guide.