Greetings Bill:
There are two principal state forestry programs available in Illinois: Forestry Development Act (IFDA), > 10 acres; and the Illinois Conservation Stewardship Program (CSP), < 10 acres.
The Illinois Forestry Development Act is tailored to "timber growers" who are interested in managing their forest land for timber production in addition to other compatible stewardship goals such as wildlife, recreation, soil and water conservation, and aesthetics. The minimum acreage requirement is 10.0 acres (effective Aug. 10, 2009). This program offers the unique tax assessment of 1/6 the equalized assessed value as cropland.
The Conservation Stewardship Program is a program tailored to the more preservation-oriented landowner opposed to or unwilling to mange their forest land for timber harvesting. In contrast to IFDA, the tax assessment on CSP eligible lands is 5% fair market value.
For additional information regarding forest land tax assessments, please visit:
http://tax.illinois.gov/Publications/Pubs/Pub-135.pdf
Best of luck!