Korsakov (Russian: Корсаков; Japanese: 大泊, Ōdomari) is a town and the administrative center of Korsakovsky District of Sakhalin Oblast, Russia.

It is located 42 kilometers (26 mi) south from Yuzhno-Sakhalinsk, at the southern end of Sakhalin Island, on the coast of the Salmon Cove in the Aniva Bay.

The site was once home to an Ainu fishing village called Kushunkotan (in Russian sources, Tamari-Aniva), which was frequented by traders of the Matsumae clan from as early as 1790.

The veracity of this account is in doubt, both because Nevelskoy had ulterior motives for claiming that he was "welcomed" by the inhabitants, and also because it is not clear to what extent the Russians were able to make themselves understood.

[14] The Russians abandoned the settlement on May 30, 1854, allegedly because their presence there, at the time of the Crimean War, raised the specter of Anglo-French attack, but returned in August 1869, now renaming the town "Fort Korsakovsky," in honor of then-Governor General of Eastern Siberia Mikhail Korsakov.

Upon the ashes of Fort Korsakovsky the Japanese built a stone-clad modern city with paved streets and electricity, renaming it Ōtomari (大泊), a translation of the Ainu words "Poro-an-tomari" (big harbor).

Other Japanese sites and memorials were all destroyed, including a Shinto shrine and a monument to Prince Hirohito, who had visited Ōtomari on an inspection tour.

The factory operated on run-down equipment, possibly left over from the Japanese times, and was visible to anyone in Korsakov, as it featured a tall chimney.

It has long since gone bankrupt, and its tall chimney, no longer emitting black smoke, is the only thing that reminds one of the earlier years of Korsakov's economy.

Curiously, at the early stage of settlement (late 1890s), men in Korsakovsky outnumbered women almost by a factor of ten.

The ethnic make-up, by mother tongue, was 63.2% Russian, 10.5% Ukrainian, 7.3% Tatar, 6.3% Polish, 2.2% Japanese, 2.0% Belarusian, 1.3% German, 0.9% Lithuanian, 0.8% Circassian.

[17] The town's population was at its highest (just over 45,000) in the late 1980s, whereupon it experienced significant decline as inhabitants fled economic downturn by moving to neighboring Yuzhno-Sakhalinsk or to continental Russia.

Winter sights include skating at the city stadium and excellent cross-country skiing past the former sea weed plant (Na Agarike).

Foreign tourists from certain countries or transiting via cruise ship or air are now able to visit the town without a visa for 72 hours.

A passenger ferry service between Korsakov and Wakkanai, Hokkaidō, Japan, across the Aniva Gulf, was re-established in 2016 and is in operation between June and September of each year.