Interest earned on obligations of the State of Arkansas or any political subdivision thereof is not included in gross income.
"Obligations of the State of Arkansas" means any obligation backed by credit of the State of Arkansas.
"Any political subdivision" means a county, city or town, including special assessment districts such as road, water, sewer, reclamation, drainage, levee, school or similar districts.
2.26 Ark. Code R. 51-404(b)(6)