1820

1820 (MDCCCXX) was a leap year starting on Saturday of the Gregorian calendar and a leap year starting on Thursday of the Julian calendar, the 1820th year of the Common Era (CE) and Anno Domini (AD) designations, the 820th year of the 2nd millennium, the 20th year of the 19th century, and the 1st year of the 1820s decade.

As of the start of 1820, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.