Industrial Hemp Farming Act of 2005 - Amends the Controlled Substances Act to exclude industrial hemp from the definition of "marihuana." Defines "industrial hemp" to mean the plant Cannabis sativa L. and any part of such plant with a delta-nine tetrahydrocannabinol concentration that does not exceed .3 percent on a dry weight basis. Grants a state regulating the growing and processing of industrial hemp exclusive authority, in any criminal or civil action or administrative proceeding, to determine whether any such plant meets that concentration limit.