A mill is simply 1/1000th of anything. In the case of property values, a mill is 1/1000 of a property's taxable value. To answer the question, "How much is a mill worth?" you take 1/1000 (or.001) times the taxable value of your property.
Taxable value is calculated using the "True and Full' value of your property and multiplying it either by 4.5% for residential properties or 5% for agricultural and commercial properties. For example, a $200,000 home would have a taxable value of $9,000 ($200,000 X .045 = $9,000). One mill of this same house would be $9 ($9,000 X .001 = $9). If you hear an official discuss mill values in large dollar amounts, they are more than likely talking about the total revenue brought into the budget for each mill assessed.
For a more in-depth explanation of property taxes and mills, go to the North Dakota Association of Counties webpage.
Most libraries receive their primary funding through a city or county mill levy. This means that they must follow the guidelines laid out in NDCC §57-15-06.7 and §57-15-10. The local support of a library through a mill is also important for maintaining State Aid Eligibility as laid out in NDCC §54-24.2-02.2. For more information on State Aid to Public Libraries eligibility and amounts, see the State Aid tab of this guide.
The process for raising the mill levy for the library is laid out in NDCC §40-38-02 #5. It includes either a motion of the governing body or a petition of residents to move the issue to a vote. In order to pass, 60% of qualified electors need to vote in favor of increasing the levy for public library service.
Attorney General Opinion 2006-L-07 discusses joint city-county library services as it relates to mills.
Have you ever been told that you’re a “Home Rule City” or "Home Rule County" and didn’t have any idea what that meant? You’re not alone. 88% of public libraries in North Dakota reside in a city or county with a home rule charter. Let’s break it down—
Typically, city and county governments need to follow the basics of state law, but if the municipality has passed a home rule charter, they are given the freedom to implement ordinances in regards to finances, property taxes, and other taxes as laid out in NDCC §40-05.1-06. This means that, if specified in the home rule charter, a municipality may levy more than 4 mills for library service. (The 4 mill levy limit is prescribed in NDCC §57-15-06.7 and §57-15-10. There are additional constraints if you are funded by both a city and a county or a multi-city agreement.) Home rule communities may also amend the number of trustees serving on their boards if it is prescribed in their home rule charter.
Attorney General Opinion 2006-L-07 also discusses raising a mill in a home rule city or county.