Allen County Property Tax Bills Are In The Mail04/09/2021 Allen County property tax bills will be mailed today, April 9. Allen County Treasurer William Royce says the due date for the first installment is Monday, May 10th. Both the spring and fall remittance coupons are included in the bill. There will be no fall mailing. Last year Governor Holcomb ordered an extension of the due date because of the pandemic, but there is no extension this year. Spring payments received after May 10 are subject to a late fine.