Commencing July 1, 1977, each city within its corporate boundaries and each county within the unincorporated area of the county shall levy a tax of at least six and three-fourths cents per thousand dollars of assessed value on the taxable property or at least the monetary equivalent thereof when all or a portion of the funds are obtained from a source other than taxation, for the purpose of providing financial support to the public library which provides library services within the respective jurisdictions.