S.D. Codified Laws § 7-3-7
If a new county is organized or created out of an organized county in this state or in counties which have been divided and the liabilities and assets of the county as it existed prior to the division of the county have not been apportioned and divided by the board of county commissioners of the original county and the newly organized portion, the auditor-general of this state shall make an inventory of all of the assets and liabilities of the original county and the new county or counties and estimate the value and amount of the assets and liabilities. After notice to the county commissioners of the counties affected, the auditor-general shall apportion the liabilities and assets of the counties in the manner provided by law for the apportionment of bonded indebtedness.
SDCL 7-3-7