Amends the Department of Revenue Law of the Civil Administrative Code of Illinois. Requires the Department of Revenue to conduct a property tax assessment process study. Amends the Property Tax Code. Limits the increase in the assessment of any commercial or residential property to 15% over the assessed value in the previous tax year and 40% in any 3-year period. Provides that the limitation shall apply in counties with 3,000,000 or more inhabitants and may apply in other counties by ordinance or resolution of the county board. Provides that, in counties with 3,000,000 or more inhabitants, whenever the chief county assessment officer of the county substantively changes the procedure by which he or she assesses properties, the chief county assessment officer shall hold a 60-day public comment period to receive input from members of the public before the change takes effect.