Gather financial documents. Include tax returns, paystubs, financial account statements and documentation of retirement plans. Illinois divorce laws consider a spouse's retirement or pension plan when dividing martial assets.
List all property you and your spouse own, along with estimated values, and all current debts. Include all property acquired during the marriage. List the type, account numbers and current balances of all debt. Note any debt that belonged to your spouse before you married. Illinois treats debt of a spouse from before the marriage as nonmarital debt, so you're not responsible for it in the divorce.
Make a list of what you own as separate property. List all property you owned before you got married. Some of your property might not be subject to the property division even if you received it while you were married, such as an inheritance. For example, a rental property you inherited from a relative is not marital property.
Make a list of items in your household. Don't include small items, such as towels, but include expensive items, such as living room furniture and costly electronics. Larger household items are part of the marital property division in Illinois.
Document any money your spouse spent while engaging in marital misconduct. Include receipts and other supporting documents, such as phone records. Although you won't gain a legal advantage from your spouse's misbehavior, Illinois laws provide for reimbursement to the marital estate if a spouse spends money while engaging in misconduct.