I would say no, because you already know that it would not be accepted and you're trying to gimmick your way around the situation. It's a different situation than if you mailed a check on the 26th expecting it to be accepted and then there was an unexpected delay in the mail. Plus if the check is post-dated to 2018 that automatically defeats the attempt. And if the county really doesn't accept advance payments, they may return your check, or credit it to 2017 taxes and then issue you a refund will be a taxable recovery next year.
I'm asking because I have a farm business which is farmed under contract by another individual. At times he has asked us to send a check for expenses on the last day of the year, so with each of us on a cash basis, we're able to take the deduction in one year and he is able to receive those funds in the next year. In this case, when the county receives the check on January 2, 2018, they will credit it as normal. That is why I am asking -- not trying to gimmick the process.
@Hal_Al or @TaxGuyBill might have a different opinion. I just think that since you know the county won't receive the money until 2018, and would refuse a check if you walked into the office on 12/29/17, and you know these facts ahead of time, then you aren't actually spending the money in 2017. It's the opposite of constructive receipt -- constructive expense? You know the check won't be cashed and have no real intention of paying the tax in 2017, you just want to make it look like you tried.
Hers;s an example:
<a rel="nofollow" target="_blank" href="http://www.smdailyjournal.com/news/local/local-property-tax-collectors-can-t-prepay/article_084dadf4-e543-11e7-bf61-e76a15d2b443.html">http://www.smdailyjournal.com/news/local/local-property-tax-collectors-can-t-prepay/article_084dadf4-e543-11e7-bf61-e76a15d2b443.html</a>