Mae Hong Son province, also spelled Maehongson, Mae Hong Sorn or Maehongsorn, is one of Thailand's seventy-six provinces (changwat). It lies in upper northern Thailand and is the westernmost province. Neighboring provinces are Shan State of Myanmar, Chiang Mai and Tak. To the west, the province borders Kayin State and Kayah State of Myanmar.

Kayah State, or Karenni State, is a state of Myanmar. Situated in eastern Myanmar, it is bounded on the north by Shan State, on the east by Thailand's Mae Hong Son Province, and on the south and west by Kayin State. It lies approximately between 18° 30′ and 19° 55′ north latitude and between 96° 50′ and 97° 50′ east longitude. The area is 11,670 km2 (4,510 sq mi). Its capital is Loikaw. The estimated population in the 2014 Myanmar Census was 286,738, the smallest among Myanmar's seven states. It is inhabited primarily by the Karenni ethnic group, also known as Red Karen or Kayah, a Sino-Tibetan people.