The term "taxing district" as herein used shall be held to mean and embrace all counties, cities, towns, townships, port districts, school districts, metropolitan park districts or other municipal corporations which now, or may hereafter exist.
The term "the last assessed valuation of the taxable property in such taxing district" as used herein shall be held to mean and embrace the aggregate assessed valuation for such taxing district as placed on the last completed and balanced tax rolls of the county next preceding the date of contracting the debt or incurring the liability.