Leningrad was a city located on Earth in the former nation-state of Russia. The city was named for the communist revolutionary Vladimir Lenin.
In the 21st century, this city was known as St. Petersburg. In 2059, Wendy Ruiz Raymond was born in this city. (TNG: "The Neutral Zone")
In 2268, Pavel Chekov claimed that Scotch whisky had been invented by a "little old lady" from Leningrad. (TOS: "The Trouble with Tribbles")
Expressing his amazement over the planet Mudd, Pavel Chekov remarked that "this place is even better than Leningrad." (TOS: "I, Mudd")
Leningrad was hit by the effects of the Whale Probe in 2286, losing all electrical power, and experiencing a cloud cover of 100% - blocking out the sun, and causing temperatures to plummet. The damage was reversed following the actions of James T. Kirk and the "HMS Bounty". (Star Trek IV: The Voyage Home)
The city was renamed St. Petersburg in 1991, four years after the movie was filmed, causing a real life retcon. The province containing the city of St. Petersburg is still named Leningrad Oblast.