thumb|Petroglyphs near Petersburg, Mitkof Island, Alaska.
Mitkof Island is an island in the Alexander Archipelago in southeast Alaska between Kupreanof Island to the west and the Alaskan mainland to the east. It is approximately wide and long with a land area of , making it the 30th largest island in the United States. Much of the island is managed as part of the Tongass National Forest.
The island is relatively flat with numerous muskegs. The highest point is Crystal Mountain .
The city of Petersburg is on the north end of the island. It's the headquartered of the Petersburg Indian Association, a federally recognized Tlingit tribe.
History
The island has historically been the home of the Séet Ká Ḵwáan Tlingit people.
The first European to sight the island was James Johnstone, one of George Vancouver's officers during his 1791-95 expedition, in 1793. The island is shown as separate from Kupreanof Island in an 1844 Russian chart, while the name was published in 1848 on a Russian Hydrographic Department chart as "Os(trov) Mitkova" for an Admiral Prokofy Mitkov.