Any county or municipality in the State or any agency or institution thereof shall have the option of participating under the provisions of this article but no county, municipality, agency or institution thereof shall be covered by the workers’ compensation insurance provided in this article until payment of the annual charge provided in this title shall have been made to the fund, nor shall any county, municipality, agency or institution thereof be covered by this insurance after the lapse of the period for which the annual charge has been paid. The director shall notify each county, municipality, agency or institution thereof at least thirty days before the expiration date of its coverage in order that the county, municipality, agency, or institution may keep its insurance in force continuously.