What is the meaning of suffix sex as in Sussex or Middlesex?

The suffix "sex" in place names like Sussex and Middlesex comes from the Old English word "sēxe", which means "people" or "tribe".

Therefore, Sussex literally translates to "people of the South Saxons", and Middlesex translates to "people of the middle Saxons".

This suffix is common in place names across England, indicating the presence of a particular tribe or group of people in that region.