Following approval of the consolidation of county or township offices and prior to January 15 of the year in which the general election is held for consolidated offices, the county boards of each county included within such consolidation shall, by joint or concurrent action, establish the salary to be paid to the holder of the consolidated office and shall apportion such salary among the counties in the proportion that the population in each county bears to the population in all such counties or according to the consolidation agreement. In establishing salaries for a consolidated office, the county boards shall use the population of the counties involved according to the most recent federal decennial census. Minimum annual salaries are established by sections 23-1114.02 to 23-1114.07, and the combined population of the counties involved shall be used to determine the class pursuant to section 23-1114.01. The county boards shall further agree upon the actual payment of such salary by a single county and the monthly remittance to such paying county of the proportionate share of each of the other counties.