There are contradictory sources concerning Ogiński's birth and death. They are more or less equally divided between 25 September 1765 and 7 October 1765 for his birth, which probably stem from a conversion between the old style (Julian) calendar in use in the Russian Empire, and the new style (Gregorian) calendar used in western Europe, which then differed by 11 days in the 18th century, and 12 days in the 19th century. However, at the time Ogiński's birthplace of Guzów was in the Polish-Lithuanian Commonwealth, which used the new-style dates, and his tombstone  confirms 7 October to be correct. It looks as though 25 September was an old-style date, calculated on the incorrect assumption that Guzów was then part of Russian Poland, and was 12 (rather than 11) days behind the new-style calendar.
The same tombstone shows 18 October 1833 as his death, while other sources give 15 October (e.g. Grove, Polish Wikipedia), and others 10 October (e.g. English Wikipedia). I've used 18 October, on the basis that the tombstone is more likely to be correct, unless more firm evidence comes to light — P.davydov 07:00, 27 March 2009 (EDT)