Under Illinois law, the Treasurer's Office is required to conduct two types of tax sales in which delinquent property taxes are sold.
The first is the Annual Tax Sale, held once a year. If property taxes for the immediately preceding tax year are delinquent on a parcel, they are offered for sale to tax purchasers at the Annual Tax Sale. The sale may be held any time from the fall of that year to the fall of the following year. Please check this website periodically for the announcement of the date.
Those interested must meet a set of qualifications to participate in the Annual Tax Sale. They must complete registration materials and provide collateral or a bond. The registration materials include rules for the conduct of a tax sale.
The biennial Scavenger Sale (conducted in odd-numbered years) offers taxes on properties that have delinquencies on three or more years that were not purchased at an Annual Tax Sale.
For a complete understanding of the distinctions between these sales and how to proceed to tax deed, read 35 ILCS (Illinois Compiled Statutes) 200/1-1, et. seq. This information can be found in any law library.