Regarding Federal Tax Law passed in 2017, in Wyoming you are unable to prepay your 2018 tax for credit on your 2017 income tax.
According to the IRS—
"A prepayment of anticipated real property taxes that have not been assessed prior to 2018 are not deductible in 2017. State or local law determines whether and when a property tax is assessed, which is generally when the taxpayer becomes liable for the property tax imposed."
The 2018 Assessments will be available in April, 2018, and per Wyoming Statute, the Mill Levy and Tax Roll will not be approved until August, 2018.
More information can be found here.
200 N. Center
Casper, WY 82601
P.O. Box 2290
Casper, WY 82602