The county board shall provide for the manner in which such regulations and restrictions and the boundaries of such districts shall be determined, established, enforced, and, from time to time, amended, supplemented, or changed. No such regulation, restriction, or boundary shall become effective until after public hearings are held by both the county planning commission and county board in relation thereto, when its parties in interest and citizens shall have an opportunity to be heard. Notice of the time and place of such hearing shall be given by the publication thereof in a legal newspaper of general circulation in such county one time at least ten days prior to such hearing. Notice of the time and place of such hearing shall also be given in writing to the chairperson of any municipal, county, or joint planning commission in the State of Nebraska which has jurisdiction over land within three miles of the property affected by such action. In the absence of a planning commission, such notice shall be given to the clerks of units of local government in the State of Nebraska having jurisdiction over land within three miles of the property affected by such action.