On the second Tuesday after the election under section 23-201 adopting township organization in any county, the county attorney, county clerk, and county treasurer of the county shall meet at the county seat of such county and shall, within three days from and after the first day of meeting, divide such county into seven districts to be known as supervisor districts. Such districts shall be divided as nearly as possible with regular boundary lines and in regular and compact form and shapes, and each of such districts shall as nearly as possible have the same number of inhabitants as any other district. No voting precinct shall be divided by any such district, except that in counties having cities of more than one thousand inhabitants as determined by the most recent federal decennial census or the most recent revised certified count by the United States Bureau of the Census and when such cities have more inhabitants than the average outlying district, the county board shall add enough contiguous territory to such city so that the inhabitants in such city and contiguous territory equal the inhabitants of two of the other districts. The county attorney, county clerk, and county treasurer shall then divide the tract thus segregated into two supervisor districts with population as nearly equal as possible, and when so divided, each of the districts shall elect one supervisor who shall reside in such supervisor district and be nominated and elected by the registered voters residing in that district. If any such city has more than the requisite inhabitants for two supervisor districts, then sufficient outlying territory may be added to such city to make three supervisor districts. The supervisor in each supervisor district in such city shall reside in such supervisor district and be nominated and elected by the registered voters residing in that supervisor district. The remainder of the county outside of such city districts shall be divided so as to create a total of seven supervisor districts, except that if any county under township organization has gone to an at-large basis for election of supervisors under section 32-554, the board of supervisors of such county may stay on the at-large voting basis.