The Pilgrims landed in Plymouth in December 1620. After a 66-day voyage, the Mayflower arrived in New England on November 11, 1620. Due to dangerous shoals and poor winds, they initially sought shelter at Cape Cod. The ship anchored in Plymouth Harbor on December 18, 1620, and the colonists began building their town. The first expedition took a shallop ashore on December 21, 1620, which is considered the time when the Pilgrims came ashore at Plymouth. The Pilgrims began constructing their settlement shortly after, though many lived on the ship through the harsh first winter.
Plymouth Rock is traditionally associated with their landing, but the Pilgrims themselves did not mention it, and it was first identified as significant over 100 years later. The actual act of landing on Plymouth Rock is not documented and is considered more of a later legend.
In summary, the Pilgrims landed at Plymouth Harbor and came ashore around December 21, 1620.