1. For the purpose of promoting health, safety, morals, comfort or the general welfare of the unincorporated portion of counties, to conserve and protect property and building values, to secure the most economical use of the land, and to facilitate the adequate provision of public improvements all in accordance with a comprehensive plan, the county commission in all counties of the first class, as provided by law, except in counties of the first class not having a charter form of government, is hereby empowered to regulate and restrict, by order, in the unincorporated portions of the county, the height, number of stories and size of buildings, the percentage of lots that may be occupied, the size of yards, courts and other open spaces, the density of population, the location and use of buildings, structures and land for trade, industry, residence or other purposes, including areas for agriculture, forestry and recreation.

2. The provisions of this section shall not apply to the incorporated portions of the counties, nor to the raising of crops, livestock, orchards, or forestry, nor to seasonal or temporary impoundments used for rice farming or flood irrigation. As used in this section, the term “rice farming or flood irrigation” means small berms of no more than eighteen inches high that are placed around a field to hold water for use for growing rice or for flood irrigation. This section shall not apply to the erection, maintenance, repair, alteration or extension of farm structures used for such purposes in an area not within the area shown on the flood hazard area map. This section shall not apply to underground mining where entrance is through an existing shaft or shafts or through a shaft or shafts not within the area shown on the flood hazard area map.

3. The powers by sections 64.010 to 64.160 given shall not be exercised so as to deprive the owner, lessee or tenant of any existing property of its use or maintenance for the purpose to which it is then lawfully devoted except that reasonable regulations may be adopted for the gradual elimination of nonconforming uses, nor shall anything in sections 64.010 to 64.160 interfere with such public utility services as may have been or may hereafter be specifically authorized or permitted by a certificate of public convenience and necessity, or order issued by the public service commission, or by permit of the county commission.

4. For the purpose of any zoning regulation adopted under the provisions of sections 64.010 to 64.160, the classification of single-family dwelling or single-family residence shall include any home in which eight or fewer unrelated mentally or physically handicapped persons reside, and may include two additional persons acting as houseparents or guardians who need not be related to each other or to any of the mentally or physically handicapped persons. The classification of single-family dwelling or single-family residence shall also include any private residence licensed by the children’s division or department of mental health to provide foster care to one or more but less than seven children who are unrelated to either foster parent by blood, marriage or adoption. A zoning regulation may require that the exterior appearance of the home and property be in reasonable conformance with the general neighborhood standards and may also establish reasonable standards regarding the density of such individual homes in any specific single-family dwelling or single-family residence area. Should a single-family dwelling or single-family residence as defined in this subsection cease to operate for the purposes specified in this subsection, any other use of such dwelling or residence, other than that allowed by the zoning regulations, shall be approved by the county board of zoning adjustment. Nothing in this subsection shall be construed to relieve the children’s division, the department of mental health or any other person, firm or corporation occupying or utilizing any single-family dwelling or single-family residence for the purposes specified in this subsection from compliance with any ordinance or regulation relating to occupancy permits except as to number and relationship of occupants or from compliance with any building or safety code applicable to actual use of such single-family dwelling or single-family residence.

5. Except in subsection 4 of this section, nothing contained in sections 64.010 to 64.160 shall affect the existence or validity of an ordinance which a county has adopted prior to March 4, 1991.