Last month, a bill was introduced in the Illinois General Assembly to create the “Local Accessory Dwelling Unit Act.” HB4869 If passed, this legislation would prohibit all units of local government in the state from prohibiting the building or use of an accessory dwelling unit. The bill would allow the local government to provide reasonable regulations relating to the size and location of accessory dwelling units except to the extent that the regulation would have the effect of prohibiting these units, sometimes referred to as “coach homes” or “granny flats.” The bill would preempt home rule powers.
“Accessory dwelling unit” is defined to include any attached or detached residential dwelling unit that provides complete independent living facilities for one or more persons and is located on a lot with a primary residence. These accessory dwelling units would expressly include efficiency units and manufactured homes. 
It’s not clear how municipalities square the limitations in this bill with the zoning authority that municipalities have under state law since the bill appears to create a stand-alone act outside of the Zoning Enabling Act. The bill also fails to address issues such as lot size, density, parking, access, single family zoning, and other factors that might impact the viability of a requirement that municipalities permit two homes on every lot. 
Because the elimination of single-family zoning in Illinois would have a significant impact on residential zoning and districts throughout the state, we will keep you informed of this bill’s progress.