The boundaries of counties may be changed by taking territory from a county and attaching it to an adjoining county, and new counties may be established out of territory of one or more existing counties. A new county shall contain at least 400 square miles and have at least 4,000 inhabitants. A proposed new county must have a total estimated market value of at least 35 percent of (i) the total estimated market value of the existing county, or (ii) the average total estimated market value of the existing counties, included in the proposition. The determination of the estimated market value of a county must be made by the commissioner of revenue. An existing county shall not be reduced in area below 400 square miles, have less than 4,000 inhabitants, or have a total estimated market value of less than that required of a new county.

No change in the boundaries of any county having an area of more than 2,500 square miles, whether by the creation of a new county, or otherwise, shall detach from the existing county any territory within 12 miles of the county seat.