Except for single-family homeowners working on their own personal residence, the City of East St. Louis requires all electricians to be licensed. The State of Illinois requires plumbers and roofers to be licensed.
The State of Illinois requires that all buildings other than detached single and two family dwellings on their own lot be designed by and the construction plans sealed by an Illinois Licensed Architect, Structural Engineer or Professional Engineer depending on the type of project. See applicable state statute for more detail. This is enforced by the State of Illinois Department of Professional Regulation.