The Diomede Islands lie in the middle of the Bering Strait between Russia and the United States. Though the two islands are only about 2.4 miles apart and clearly a single group, they are separated by the International Dateline which also marks the international border between Russia and the United States. Big Diomede is owned by Russia and Little Diomede is owned by the USA. They are sometimes called Tomorrow and Yesterday respectively because they straddle the dateline.
Their official separation into Russian and US Territiories was set by the 1867 treaty finalizing the sale of Alaska by Russia to the United States. That treaty includes the text,
"The western limit within which the territories and dominion conveyed, are contained, passes through a point in Behring's straits on the parallel of sixty-five degrees thirty minutes north latitude, at its intersection by the meridian which passes midway between the islands of Krusenstern, or Ignalook, and the island of Ratmanoff, or Noonarbook, and proceeds north, without limitation, into the same Frozen Ocean."
The treaty references Krusenstern and Nunarbuk which were alternative Russian names for the islands as well as names used but the local native population. There is a small Inupiat Eskimo population on Little Diomede Island in a small village on its Western shore. Big Diomede has a small Russian Military population but the native population on Big Diomede was relocated to the mainland by Russia.
The islands gained a bit of unexpected fame during the 2008 US Presidential Election. Although you really can see Russia from Alaska here, it became the subject of a Saturday Night Live satire with Tina Fey playing the role of Sarah Palin in her less than successful bid for the Vice President.