415 ILCS 5/3.103: 100-year floodplain.

"100-year floodplain" means the lowland and relatively flat areas adjoining inland and coastal waters, including flood-prone areas of offshore islands, that are inundated by a 100-year flood. For the purposes of this Act, including for the purposes of granting permit and license applications filed or pending prior to the effective date of this amendatory Act of the 96th General Assembly, an area shall be deemed by operation of law not to be within the 100-year floodplain if the area lies within an area protected by a federal levee and is located in a flood prevention district established in accordance with the Flood Prevention District Act; provided, however, that an area that lies within a flood prevention district established in accordance with the Flood Prevention District Act shall be deemed by operation of law to be within the 100-year floodplain if, according to the currently adopted federal flood insurance rate map, the area is subject to inundation by a 100-year flood from bodies of water other than the Mississippi River.