Some homeowners -- particularly those with high property taxes -- are spending this last week of 2017 in lines at county offices looking to pre-pay 2018's tax bill before the end of the year.

That's because the new tax bill that passed last week puts a cap on the amount you can deduct for state, local and property taxes at $10,000. Currently the deduction is unlimited. In some high-tax states like New York, New Jersey and Maryland, that means some homeowners will be paying a lot more in taxes.

The three counties with the highest median tax bills in the country -- Nassau County, Rockland County and Westchester County, which are all in New York -- have median tax bills exceeding the $10,000 cap, according to the Tax Foundation.

While some jurisdictions have long allowed for pre-payment, others are scrambling, working to ensure that those who want to pre-pay can -- even if the jurisdiction can't necessarily guarantee the pre-payment will be deductible.

Montgomery County, Maryland, just outside of Washington DC, did not previously allow for pre-payment. That rubbed some homeowners the wrong way after the tax bill was signed into law. Especially when their neighbors in nearby counties and jurisdictions, including Fairfax county in Virginia and Washington DC, could pay ahead.

Hundreds of people in line at the Fairfax Govt Center. They'll be prepaying their property tax, since the new tax law caps property tax deductions at $10k. pic.twitter.com/Z4sKUoIBnh — Neal Augenstein (@AugensteinWTOP) December 26, 2017

"It just never came up," said George Leventhal, Montgomery County council member. "No one was saying, 'Please let me make early payment of a bill I don't owe.' Wise cash management suggests you should pay closer to the due date, not farther away. But because of this change, it seems it could be possible that people could derive some benefit and deduct their property taxes for next year in 2017."

The county broke its winter recess and called a special session on Tuesday, the day after Christmas, passing a bill 7 to 1 in favor of allowing residents to pre-pay their 2018 tax bills.

Are you trying to pre-pay your taxes? Tell CNNMoney how it's going

Leventhal was among the majority voting for it. But says he is still ambivalent about its effect for homeowners.

"There are so many moving pieces that even now that it has passed, we're not in a position to assure our residents that these payments are going to be deductible," said Leventhal. Ultimately it will be up to the Internal Revenue Service to make that determination.

But the county felt a need to respond to a demand to pre-pay. Leventhal says that nearly half of the county's taxpayers will have more than $10,000 in combined state and local taxes.

Still, that's a lot of cash to have ready at a moment's notice to throw at taxes, without any assurance of getting the deduction. But some homeowners have determined the risk is worth it.

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How to pre-pay your taxes

To pre-pay your own taxes within the next few days, you will need to check with your local jurisdiction to find out if it even allows for pre-payment and to learn more about the process.

Here are some things to keep in mind.

If you pre-pay you're not guaranteed you'll be able to deduct the payment. It will be up to the Internal Revenue Service to determine whether pre-payment of 2018 property taxes may be deducted for federal, state or local income tax purposes.

If you are currently getting your taxes escrowed, you'll need to work with your escrow agency or mortgage company on any future adjustments to your escrow account. Usually escrowed taxes are a matter for the taxpayer and the taxpayers' escrow agency to resolve.

Many jurisdictions may have either a pre-payment application or a requirement that a notice of intent to pay early accompanies payment.

Some areas will allow online payments. Anyone paying by check after today may have a difficult time since often the check must clear by the end of the year.

In some areas, homeowners are encouraged to avoid mailing payments, since they have to be received and recorded by the end of the year. Yet, other jurisdictions allow mailed payment to count so long as it is postmarked by Dec. 31.