(10 ILCS 91/20)
Sec. 20. Definitions; exceptions; deposit; description.
(a) In this Act, all counties, census tracts, blockgroups, and blocks are those that appear on maps published by the United States Bureau of the Census for the 2010 census. The term "tract" means census tract. Legislative and Representative Districts created by this Act for the purpose of electing Senators to the Illinois Senate and Representatives to the Illinois House of Representatives shall not be altered by operation of any other statute, ordinance, or resolution.
(b) In this Act, census tracts are identified by an up to 4-digit integer number and may have an optional 2-digit suffix; for example 1457.02 or 23. The census tract codes consist of 6 digits with an implied decimal between the fourth and fifth digit corresponding to the basic census tract number but with leading zeroes and trailing zeroes for census tracts without a suffix. The tract number examples 1457.02 and 23 would have codes of 145702 and 002300, respectively.
(c) Any part of Illinois that has not been described as included in one of the Districts described in this Act is included within the District that (i) is contiguous to the part and (ii) contains the least population of all districts contiguous to the part according to the 2010 decennial census of Illinois.
(d) If any part of Illinois is described in this Act as being in more than one District, the part is included within the District that (i) is one of the Districts in which that part is listed in this Act, (ii) is contiguous to that part, and (iii) contains the least population according to the 2010 decennial census of Illinois.
(e) If any part of Illinois (i) is described in this Act as being in one District and (ii) is entirely surrounded by another District, then the part shall be incorporated into the District that surrounds the part.
(f) If any part of Illinois (i) is described in this Act as being in one District and (ii) is not contiguous to another part of that District, then the part is included within the contiguous District that contains the least population according to the 2010 decennial census of Illinois.
(g) The Speaker of the House, the Minority Leader of the House, the President of the Senate, and the Minority Leader of the Senate shall by joint letter of transmittal present to the Secretary of State for deposit into the State Archives an official set of United States Bureau of the Census maps and descriptions used for conducting the 2010 census, and those maps shall serve as the official record of all counties, census tracts, blockgroups, and blocks referred to in this Act.
(h) The State Board of Elections shall prepare and make available to the public a metes and bounds description of the Legislative and Representative Districts created under this Act.
(Source: P.A. 97-6, eff. 6-3-11.)