The county clerk of each county in which any rural fire protection district or districts have been organized under the provisions of Chapter 35 prior to April 28, 1949, shall forthwith designate a time and place for a hearing before the county board of such county and shall give due notice thereof in the manner prescribed by section 35-504. At the time and place so fixed the county board shall meet and all persons interested shall have opportunity to be heard. Thereupon, the county board shall consider the general rural fire protection policy for the county as a whole and shall determine the boundaries of the district or districts, whether as existing prior to such determination or otherwise, and shall make a written order of such determination which shall be filed in the office of the county clerk. Thereafter, such district or districts shall be deemed to be organized and operating under sections 35-501 to 35-517. Nothing herein contained shall impair, affect, or discharge any previously existing contract, obligation, lien, or charge of the district or districts.