1642 (MDCXLII) was a common year starting on Wednesday of the Gregorian calendar and a common year starting on Saturday of the Julian calendar, the 1642nd year of the Common Era (CE) and Anno Domini (AD) designations, the 642nd year of the 2nd millennium, the 42nd year of the 17th century, and the 3rd year of the 1640s decade. As of the start of 1642, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.