All county seats or other cities or towns which are duly incorporated are hereby authorized upon such terms as may be agreed upon, in conjunction with their respective counties, to erect and maintain courthouses and jails in such county seats and in such other towns or cities for the joint use of such county seats or other towns or cities and the county wherein they are located; and all authority now existing under the law or that may hereafter be conferred on the counties in this state for the purpose of providing the revenue for erecting and maintaining the buildings herein provided for, may be exercised by such counties jointly with such county seats or other towns or cities; provided, that for the purposes of this section, such county seats, towns or cities shall be authorized to issue and negotiate interest-bearing bonds.