September 15 is the 258th day of the year (259th in leap years). 107 days remain until the end of the year.
"The simplest explanation is always the most likely."
Born today
Agatha Christie, 1890, British writer
Observances
Cry of Dolores, celebrated on the eve of Independence Day (Mexico).
Earliest day on which Father's Day can fall, while September 21 is the latest; celebrated on the third Sunday in September. (Ukraine)
Earliest day on which German-American Steuben Parade can fall, while September 21 is the latest; celebrated on the third Saturday in September. (United States, especially New York City)
Earliest day on which POW/MIA Recognition Day can fall, while September 21 is the latest; celebrated on the third Friday in September. (United States)
Earliest day on which Prinsjesdag can fall, while September 21 is the latest; celebrated on the third Tuesday in September. (Netherlands)
Earliest day on which Respect for the Aged Day can fall, while September 21 is the latest; celebrated on the third Monday in September. (Japan)
Engineer's Day (India)
Independence Day, celebrates the Act of Independence of Central America from Spain in 1821 of Guatemala (a Patriotic Day), El Salvador, Honduras, Nicaragua, and Costa Rica.
International Day of Democracy
Knowledge Day (Azerbaijan)
Silpa Bhirasri Day (Thailand).
The beginning of German American Heritage Month, celebrated until October 15
The beginning of National Hispanic Heritage Month, celebrated until October 15 (United States)