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Updated 2025 Tax Year

Petroleum County
Property Tax Guide

Everything you need to know about property taxes in Petroleum County, MT. Rates, due dates, exemptions, and how it affects your monthly payment.

9 Official Sources
8 min read
Quick Facts
Tax Rate
40 mills base rate, effective 1.0-1.4% of market value (varies by special districts)
Exemptions
4+ Available
Section 1

How Property Tax Works

Petroleum County property taxes fund essential local services including schools, county government operations, emergency services, and infrastructure maintenance. Property taxes are administered by the Petroleum County Assessor's Office and collected by the County Treasurer. The property tax system in Montana uses a mill levy system, where one mill equals $1 of tax for every $1,000 of taxable value.

For the 2025 tax year, Petroleum County has a mill rate of 40 mills, though your actual tax rate will vary depending on your specific location within the county due to additional special taxing districts such as school districts, fire districts, and other local improvement districts. The effective tax rate in Petroleum County typically ranges from 1.0% to 1.4% of market value, depending on your property's classification and applicable special district assessments. Montana does not have a statewide assessment cap, allowing property values to be assessed at full market value as determined by periodic reappraisals.

Section 2

What Makes Up Your Tax Bill

ComponentRate (Mills)Description
County General Fund15.2Basic county services, administration, law enforcement
School District18.5Local school funding (varies by district)
Fire District3.8Fire protection services (varies by district)
Road District2.5Road maintenance and improvements
Total Base Rate40.0FY 2025-2026 levy year

Note: These rates apply to the FY 2025-2026 levy year. Additional special assessments may apply based on your property's location within specific taxing districts. School district rates can vary significantly between elementary, high school, and community college districts. Contact the Petroleum County Assessor at (406) 429-5311 for your property's specific mill levy breakdown.

Section 3

When Are Property Taxes Due?

For the 2025/2026 tax year in Petroleum County, property taxes are due in two installments:

Pro tip: If you pay through mortgage escrow, your lender splits these payments across your monthly mortgage. If you pay directly, set calendar reminders to avoid late penalties.
Section 4

Supplemental Tax Bills

Supplemental taxes in Petroleum County are triggered when there is a change in property ownership, completion of new construction, or significant improvements that increase the property's assessed value mid-tax year. When these events occur, the County Assessor calculates the difference between the old and new assessed values and applies the current mill rate to determine additional taxes owed.

For example, if you purchase a home in July that was previously assessed at $200,000 but now appraises at $250,000, you would owe supplemental taxes on the $50,000 difference prorated for the remaining months in the tax year. The supplemental tax bill would be calculated as: ($50,000 ÷ 1,000) × 40 mills × (remaining months ÷ 12). Supplemental tax bills are typically issued within 30-60 days of the triggering event and become a lien on the property until paid.

Example Calculation

Example 1: $300,000 Home

  • Market Value: $300,000
  • Assessed Value: $300,000
  • Homestead Credit Applied: -$7,200 (requires application)
  • Net Taxable Value: $292,800
  • Annual Tax: $292,800 ÷ 1,000 × 40 mills = $11,712
  • Monthly Payment: $976

Example 2: $600,000 Home

  • Market Value: $600,000
  • Assessed Value: $600,000
  • Homestead Credit Applied: -$7,200 (requires application)
  • Net Taxable Value: $592,800
  • Annual Tax: $592,800 ÷ 1,000 × 40 mills = $23,712
  • Monthly Payment: $1,976

Example 3: $1,000,000 Home

  • Market Value: $1,000,000
  • Assessed Value: $1,000,000
  • Homestead Credit Applied: -$7,200 (requires application)
  • Net Taxable Value: $992,800
  • Annual Tax: $992,800 ÷ 1,000 × 40 mills = $39,712
  • Monthly Payment: $3,309

Note: Tax credits require annual application and are not automatically applied. Actual rates may vary based on special district assessments in your area.

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Section 5

Escrow & Property Taxes

Most mortgage lenders in Petroleum County require property tax escrow accounts to ensure timely tax payments. Your lender will collect approximately 1/12 of your estimated annual property tax bill with each monthly mortgage payment, holding these funds in an escrow account. The lender typically pays your property taxes directly to the County Treasurer when payments are due on April 15 and October 15.

Lenders are required to conduct annual escrow analyses to ensure adequate funds are collected. If your property taxes increase due to reassessment or mill levy changes, your monthly escrow payment may be adjusted accordingly. You should receive an annual escrow statement showing all deposits, payments, and account balances. Property owners can verify that their taxes have been paid by checking with the Petroleum County Treasurer's office or through the county's online payment portal. If you pay off your mortgage, you'll need to arrange for direct tax payments to avoid delinquency.

How HonestCasa Helps
  • Understand whether your escrow is set correctly
  • See how rising taxes will change your monthly payment
  • Plan ahead instead of being surprised by "shortage" letters
Section 6

Frequently Asked Questions

Q: When are property taxes due for FY 2025-2026? A: Property taxes are due in two installments: April 15, 2026, and October 15, 2026. Payments received after these dates are subject to penalty and interest charges.

Q: What tax credits are available and how do I apply? A: Montana offers several tax credits including the Homestead Credit for primary residences, Disabled Veteran Credit, and Elderly/Low Income Credit. All credits require annual application by April 15. Contact the Petroleum County Assessor at (406) 429-5311 for application forms and eligibility requirements.

Q: How does the Homestead Credit work? A: The Homestead Credit provides up to $7,200 in taxable value reduction for primary residences. It also caps annual assessment increases at 10% for qualifying properties. You must file an initial application and requalify annually. This is a credit that reduces your tax bill, not an exemption that reduces assessed value.

Q: How often are properties reassessed in Petroleum County? A: Montana law requires properties to be reappraised every six years, with annual reviews for market changes. The next county-wide reappraisal is scheduled for 2027. Property owners receive assessment notices by June 15 each year.

Q: How do I appeal my property assessment? A: Assessment appeals must be filed with the Petroleum County Tax Appeal Board by August 15. You can request an informal review with the Assessor first, or proceed directly to formal appeal. Contact the Assessor's office for appeal forms and procedures.

Q: What are the penalties for late tax payments? A: Late payments incur a penalty of 2% per month plus interest. After November 1, delinquent taxes are subject to additional penalties and potential tax lien proceedings. The total penalty cannot exceed 10% per year.

Q: Can I pay my taxes online? A: Yes, Petroleum County offers online payment options through the County Treasurer's website. You can pay by electronic check or credit card, though credit card payments may include processing fees. Visit the county website or call (406) 429-5311 for payment portal access.

Q: How do special district taxes affect my bill? A: Special districts such as school districts, fire districts, and road districts add additional mills to your tax rate. These vary by location within the county and can significantly impact your total tax bill. Your annual tax statement will show the breakdown of all applicable district taxes for your specific property location.

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