765 ILCS 505/7

When the owner of any land shall convey, by deed or lease, any gas, oil, coal or other minerals therein, such conveyance shall be considered as so separating such gas, oil, coal or other minerals from the land that the same shall be taxable separately, and any sale of the land for any tax or assessment shall not include or affect such conveyance of the gas, oil, coal or other minerals.