Once a purchaser has paid the amount advertised in the newspaper for a property and received a Certificate of Purchase (CP), they have a lien on the property. Technically, the purchaser doesn't have to do anything else. If the property owner redeems the property (pays all the back taxes, fees and interest), the CP holder is paid and the CP is destroyed. If the property owner does not redeem the property within 4 years from the date of the tax sale, the CP holder may apply for a Tax Deed on the property. However, a CP holder has the option of paying the subsequent years' taxes on the property as they become due.
Here's an example of why you might want to do that - a landowner doesn't pay his 1999 taxes. The Treasurer's Office offers a certificate of purchase for the property at the tax sale in August, 2000. A CP holder pays the taxes, interest and fees and receives a Certificate of Purchase. In September, 2000, the 2000 taxes are billed. The CP holder may pay the taxes. If the CP holder does, they would be reimbursed the taxes plus 15% per year interest and a 3% penalty if the landowner ever redeems the property.
If the CP holder does not pay the taxes, and neither does the landowner, the Treasurer's Office will offer the property for sale again in August, 2001. A different purchaser buys a CP for the land at that sale. Once 4 years has passed for the original purchaser, he/she applies for a Tax Deed. But, in order to get a clear Tax Deed, the purchaser now has to redeem the property from the second CP holder, or as many as there were in the 4 years. That means the original CP holder must pay any subsequent CP holders the taxes plus interest, fees and penalties.
That's why most CP holders pay taxes for subsequent years - even though it's not required