A Joint and Mutual Will in Illinois is a contract between two parties (typically spouses) to dispose of their property in a certain way upon death.  The caveat, though, is that when one party dies, the Will becomes irrevocable (meaning that the surviving party will not be free to change the terms of the Joint and Mutual Will).  This can obviously lead to many complications, as circumstances oftentimes change dramatically after the death of one party and over the years that follow.  Because of this, it is not advisable to use of Joint and Mutual Wills for a married couple in estate planning.

The more standard option for married couples nowadays is for the married couple to simply make reciprocal Wills leaving their property to the surviving spouse upon death.  This allows the surviving spouse to amend his/her Will upon the death of the first spouse, and ultimately allows for more flexibility with the long-term estate plan.