Idaho constitution
Article XVIII
Section 4

No new
counties shall be established which shall reduce any county to an area of less than
four hundred (400) square miles, nor the valuation of its taxable property to less
than one million dollars ($1,000,000); nor shall any new county be formed which
shall have an area of less than four hundred (400) square miles, and taxable
property of less than one million dollars ($1,000,000), as shown by the last previous
assessment.