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1628 (MDCXXVIII)was a leap year starting on Saturday of the Gregorian calendar and a leap year starting on Tuesday of the Julian calendar, the 1628th year of the Common Era (CE) and Anno Domini (AD) designations, the 628th year of the 2nd millennium, the 28th year of the 17th century, and the 9th year of the 1620s decade. As of the start of 1628, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.
- August 4 – Thirty Years' War: With the help of Danish and Swedish reinforcements, Stralsund is able to resist Wallenstein's siege until the landing of a Danish army, led by Christian IV of Denmark, forces Wallenstein to raise the siege, and move his army to confront the new threat.
- August 10 – The Swedish 64-gun sailing ship Vasa sinks on her maiden voyage, in Stockholm Harbor.
- August 23 – George Villiers, the first Duke of Buckingham, is assassinated by John Felton.
- September 2 – Thirty Years' War – Battle of Wolgast: Wallenstein defeats Christian IV of Denmark's army.
- September 6 – Puritans settle Salem, which will later become part of Massachusetts Bay Colony.
- September 7–September 8 – Eighty Years' War – Battle in the Bay of Matanzas: Dutch admiral Piet Hein captures 16 ships of the Spanish treasure fleet. The immense booty taken brings in over 11 million guilders, part of which is used to fund the entire army of the Dutch Republic for 8 months long.
- October 22 – Abaza Mehmed Pasha surrenders to Ottoman forces, ending the Abaza rebellion.
- October 28 – The Siege of La Rochelle ends, with the surrender of the Huguenots.