1820 (MDCCCXX) was a leap year starting on Saturday (link will display the full calendar) 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 first year of the 1820s decade. At the beginning of 1820, the Gregorian calendar was only 12 days ahead of the Julian calendar, which actually stayed in localized use just before 1923.

Millennium: 2nd millennium
Centuries: 18th century19th century20th century
Decades: 1790s  1800s  1810s  – 1820s –  1830s  1840s  1850s
Years: 1817 1818 181918201821 1822 1823

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