The peninsula is separated from the rest of the island by a narrow inlet called Duncan Canal.

The island was first charted in 1793–1794 by James Johnstone and Joseph Whidbey, both part of British naval officer George Vancouver's 1791–1795 expedition.

[1] The island is named after vice admiral Ivan Antonovich Kupreianov, governor of the Russian American colonies from 1836 to 1840; the name was published in 1848 on a Russian Hydrographic Department chart as "Os(trov) Kupreyanova".

The island lies within the limits of Tongass National Forest (Petersburg Ranger District).

The Petersburg Creek–Duncan Salt Chuck Wilderness is a part of the forest that is located on the island.