Where the department of human services assigns personnel to an office located in a county for the purpose of performing in that county designated duties and responsibilities assigned by law to the department, it shall be the responsibility of the county to provide and maintain the necessary office space and office supplies and equipment for the personnel so assigned in the same manner as if they were employees of the county. The department shall at least annually, or more frequently if the department so elects, reimburse the county for a portion, designated by law, of the cost of maintaining office space and providing supplies and equipment as required by this section, and also for a similar portion of the cost of providing the necessary office space if in order to do so it is necessary for the county to lease office space outside the courthouse or any other building owned by the county. The portion of the foregoing costs reimbursed to the county under this section shall be equivalent to the proportion of those costs which the federal government authorizes to be paid from available federal funds, unless the general assembly directs otherwise when appropriating funds for support of the department.