Idaho Code § 21-405

Any county may enter into agreements with other contiguous counties or with any municipality within or without said county, and any municipality may enter into agreements with other municipalities either within or without the county wherein said municipality is located; or with any county or counties within, this state, for the purpose of the construction and maintenance of airports and for a division of the costs of such construction and maintenance and for the location of such airports and facilities connected therewith. Any county or municipality may enter into agreements with the federal government, or any of its agencies, for assistance and cooperation in the construction and maintenance of any airports and providing for the transfer of airports so constructed, to the federal government or the state of Idaho for the consideration of perpetual maintenance of said airports.