A sum (Mongolian: сум) is the second level administrative subdivision below the Aimags (provinces), roughly comparable to a County in the United States. There are 331 sums in Mongolia. Each sum is again subdivided into bags.
^Ole Bruun Precious Steppe: Mongolian Nomadic Pastoralists in Pursuit of the Market. 2006- Page 68 "The historical administrative units of aimag, sum, and bag (Khotont constitutes one of nineteen sums in Arkangai aimag) still form the bases of "