225 ILCS 705/4.23

The State shall be divided into not to exceed 22 inspection districts, the division to be made by the Mining Board. The Mining Board may change the boundaries of the districts from time to time in order to more equally distribute the labor and expenses of the several State Mine Inspectors, and may at any time reduce the number of inspection districts, and the number of State Mine Inspectors employed. However, there shall be no fewer than 16 State Mine Inspectors if there are 40 or more mines operational in the State, no fewer than 12 State Mine Inspectors if at least 30 but fewer than 40 mines are operational, no fewer than 8 State Mine Inspectors if at least 20 but fewer than 30 mines are operational, and no fewer than 4 State Mine Inspectors if at least 10 but fewer than 20 mines are operational.

For purposes of this Section, "mine" or "coal mine" means any area of land and any structures, facilities, machinery, tools, equipment, shafts, slopes, tunnels, excavations, and other property, real or personal, placed under, upon, or above the surface of the land by any person, that is used in, to be used in, or resulting from the work of extracting from that area of land bituminous coal, lignite, or anthracite from its natural deposit in the earth.