Illinois Statutes Chapter 755. Estates § 5/4-1. Capacity of testator

(a) Every person who has attained the age of 18 years and is of sound mind and memory has power to bequeath by will the real and personal estate which he has at the time of his death.

(b) Except as stated herein, there is a rebuttable presumption that a will or codicil is void if it was executed or modified after the testator is adjudicated disabled under Article XIa of this Act and either (1) a plenary guardian has been appointed for the testator under subsection (c) of Section 11a-12 of this Act or (2) a limited guardian has been appointed for the testator under subsection (b) of Section 11a-12 of this Act and the court has found that the testator lacks testamentary capacity. The rebuttable presumption is overcome by clear and convincing evidence that the testator had the capacity to execute the will or codicil at the time the will or codicil was executed. The rebuttable presumption does not apply if the will or codicil was completed in compliance with subsection (d-5) of Section 11a-18 of this Act. This subsection (b) applies only to wills or codicils executed or modified after the effective date of this amendatory Act of the 99th General Assembly.