Samosir Regency is an inland regency in North Sumatra. It was created on 18 December 2003 by splitting away the western districts of the former Toba Samosir Regency. The regency covers a land area of 1,444.25 square kilometres, including the whole of Samosir Island in the inland sea of Lake Toba. It had a population of 119,653 at the 2010 census and 136,441 at the 2020 Census; the official estimate for mid 2023 was 141,333 - comprising 70,648 males and 70,685 females. Its administrative seat is the town of Pangururan on the west coast of Samosir Island.

Toba Regency is a landlocked regency in North Sumatra. Its seat is Balige. The regency covers an area of 2,021.8 square kilometres; it had a population of 173,129 at the 2010 census and 206,199 at the 2020 Census; the official estimate as at mid 2023 was 213,850. Although landlocked, the regency includes the eastern shore of the vast inland Lake Toba.