Illinois ranks fourth in the nation among states that produce bituminous
coal, the type of coal most widely mined in the United States. Coal is
used by many manufacturing industries, by public utilities companies
that burn coal to generate electricity, and by individuals for heating
homes.
All Illinois coal deposits are found in the Pennsylvanian System. Of the
many coals, only a few are thick enough to be mined profitably. The coal
is of bituminous rank, but it varies in quality. Illinois coal reserves
in strata more than 28 inches thick are estimated at 137 billion tons
and are larger than those of any other state.
Around the edge of the coal basin where the coal lies at shallow depths,
it is commonly mined in open pits (strip mines). However, in the past,
most coal has been mined underground, and more than half of Illinois
coal is still produced from such mines.