Any person, including municipal corporations, that proposes to establish a sewage system consisting of pipelines or conduits, pumping stations, force mains or sewerage treatment plants, or any of them, or an extension of any existing system which is designed to serve three or more connections and used for conducting or treating sewage, as that term is defined in Chapter 3.1 (§ 62.1-44.2 et seq.) of Title 62.1, to serve or to be capable of serving three or more connections shall, at least sixty days prior to commencing construction thereof, notify in writing the governing body of the county in which such sewage system is to be located and shall appear at a regular meeting thereof and notify such governing body in person. However, a town proposing to construct or expand a sewage system shall not be required to provide notice in writing or in person to a county if the county itself does not operate a sewage system or provide sewerage services. In any county having a population of more than 70,000 according to the 1950 or any subsequent census or a county adjoining a city having a population of 230,000 or more according to the 1950 or any subsequent census, no extension of an existing system for the purpose of serving three or more connections shall be made by any person, firm or corporation, other than a municipal corporation, until a plan of such proposed extension, with proof of capacity to serve, has been filed with, and a permit for the extension has been obtained from, the sanitation engineer or other county official, if any, designated therefor by the board of supervisors.