70 ILCS 810/3
Any contiguous territory lying wholly within one county may be incorporated as a forest preserve district under the conditions and in the manner prescribed in Sections 1 and 2 of "An Act to provide for the creation and management of forest preserve districts in counties having a population of less than 1,000,000", approved June 27, 1913, as now or hereafter amended, and the provisions of those Sections shall apply to the same extent as if included herein.
Nothing in this Act shall impair the validity of a forest preserve district organized prior to the effective date of this Act or affect any rights, obligations or privileges of such a forest preserve district, or those of any person, existing prior to the effective date of this Act.
70 ILCS 810/3