Philistia was a confederation of cities of Sea Peoples in the Southwest Levant, which included the cities of Ashdod, Ashkelon, Ekron, Gath, Gaza and for a time Jaffa. It was populated by the Peleset or Philistines, who are believed to have been an Indo-European people who settled in Canaan around the year 1200 BC.
Exodus mentions them but they weren't there at the time of the Exodus.
The Philistines lost their independence to Tiglath-Pileser III of Assyria by 732 BC, and revolts in following years were all crushed. Later, Nebuchadrezzar II of Babylon eventually conquered all of Syria and the Kingdom of Judah, and the former Philistine cities became part of the Neo-Babylonian Empire.