What date did Seinfeld's original run end?

Seinfeld’s original run ended on May 14, 1998.

The series concluded with “The Finale,” a special 75-minute episode that aired on NBC after nine seasons. In the story, Jerry, George, Elaine, and Kramer are prosecuted for failing to help a mugging victim, allowing the show to revisit dozens of characters and grudges from earlier episodes.

The finale was written by Larry David, who had co-created Seinfeld with Jerry Seinfeld and returned for the last episode after leaving the regular production team following season 7. Andy Ackerman directed it. The broadcast was treated as a major television event and attracted approximately 76.3 million viewers in the United States.

A related source of confusion is the difference between the series ending and individual season finales. June 26, 1991, was the end of season 2; May 20, 1993, ended season 4; and April 24, 1997, was not the series finale. The final regular episode aired on May 14, 1998, after which the program continued in reruns and syndication.