Within Jacksonville city limits, chickens may only be kept in districts that are zoned as "Rural Residential" or "Agricultural." Additionally, the chickens' coop may not be located within 50 feet of your property line.
For most of use living in the city, this means that raising chickens is prohibited. However, there is an organization here that is trying change this. It's called "Hens in Jax." Below is the link. I encourage you to join the group and to sign the online petition found on the Hens in Jax website.