5 ILCS 120/2a
A public body may hold a meeting closed to the public, or close a portion of a meeting to the public, upon a majority vote of a quorum present, taken at a meeting open to the public for which notice has been given as required by this Act. A single vote may be taken with respect to a series of meetings, a portion or portions of which are proposed to be closed to the public, provided each meeting in such series involves the same particular matters and is scheduled to be held within no more than 3 months of the vote. The vote of each member on the question of holding a meeting closed to the public and a citation to the specific exception contained in Section 2 of this Act which authorizes the closing of the meeting to the public shall be publicly disclosed at the time of the vote and shall be recorded and entered into the minutes of the meeting. Nothing in this Section or this Act shall be construed to require that any meeting be closed to the public.
At any open meeting of a public body for which proper notice under this Act has been given, the body may, without additional notice under Section 2.02, hold a closed meeting in accordance with this Act. Only topics specified in the vote to close under this Section may be considered during the closed meeting.
5 ILCS 120/2a