illinois tax - SERP Analysis

https://tax.illinois.gov/

https://taxfoundation.org/location/illinois/

https://www.revenue.state.il.us/

https://capitolnewsillinois.com/news/illinois-bill-decouples-state-federal-taxes-raising-revenue-and-angering-businesses/

https://states.aarp.org/illinois/state-taxes-guide

https://apps.ilsos.gov/businessentitysearch/