Two (2) or more counties by action of their boards of supervisors may join in establishing and maintaining a regional public library system under the terms of a contract to which all of the participating counties agree. The expenses of the regional public library systems shall be apportioned between or among the counties concerned on such basis as shall be agreed upon in the contract. The public library system headquarters building shall be located at a place in one of the counties to be agreed upon by the boards of supervisors of the various counties in the regional public library system.