In no case may the amount of county funds deposited by the board of county commissioners in any one financial institution exceed the combined capital and surplus of such financial institution. In a county where the deposits to be made by the board of county commissioners of county funds exceed the combined capital and surplus of all the financial institutions in the county, qualified as depositories, the board of county commissioners nevertheless may deposit such county funds within the county upon the condition that such financial institutions furnish sufficient bonds as required in this chapter.