First Installment Tax Year 2020 property taxes are due Tuesday, March 1, Cook County Treasurer Maria Pappas reminded taxpayers. Almost 1.8 million bills were posted on cookcountytreasurer.com in early December and mailed to taxpayers in late January. “More than 70 percent of property owners have paid their taxes, including more than 207,000 taxpayers who went to our website and paid online,” Pappas said.