The ‘Legion’ and the pigs; where was it?
5
We need to start with the evidence supplied by the Greek manuscripts. We encounter the episode in three of the Gospels.

Matthew 8:28: | γεργεσηνων | 98% | (Gergesenes) AV, NKJV
| γαδαρηνων | 2% | (Gadarenes) NIV, NASB, LB, TEV, etc.

NIV footnote: “Some manuscripts Gergesenes; others Gerasenes”.

Mark 5:1: | γαδαρηνων | 95.5% | (Gadarenes) AV, NKJV
| γεργεσηνων | 4.1% | (Gergesenes)
| γερασηνων | 0.3% | (Gerasenes) NIV, NASB, LB, TEV, etc.

NIV footnote: “Some manuscripts Gadarenes; other manuscripts Gergesenes”.

Luke 8:26: | γαδαρηνων | 97% | (Gadarenes) AV, NKJV
| γεργεσηνων | 2% | (Gergesenes) TEV
| γεργεσηνων | 0.3% | (Gerasenes) NIV, NASB, LB, etc.

NIV footnote: “Some manuscripts Gadarenes; other manuscripts Gergesenes; also in verse 37”.

Luke 8:37: | γαδαρηνων | 96% | (Gadarenes) AV, NKJV
| γεργεσηνων | 3.5% | (Gergesenes) TEV
| γερασηνων | 0.3% | (Gerasenes) NIV, NASB, LB, etc.

I will begin with Mark. Jesus arrived at “the region [not ‘province’] of the Gadarenes”. Gadara was the capital city of the Roman province of Perara, located some six miles from the Sea of Galilee. Since Mark was writing for a Roman audience,* “the region of the Gadarenes” was a perfectly reasonable description of the site. Lamentably, the eclectic Greek text currently in vogue follows about five Greek manuscripts of objectively inferior quality (against at least 1,700 better ones) in reading ‘Gerasenes’ (to be followed by NIV, NASB, LB, TEV, etc.). The NIV footnote is dishonest: to use ‘some’ to describe over 1,600 manuscripts against five is a dishonest use of the Queen's English (to use ‘others’ to refer to some 60 is acceptable).
Luke also has Jesus arriving at “the region of the Gadarenes”. Since he was writing for a Greek audience, he follows Mark's example. Again NIV has a dishonest footnote. It is most likely that ‘Gerasa’ is a fiction, a ‘place’ that never existed. On the other hand, ‘Gergesa’ certainly did exist, although we no longer know the exact location. As I will explain while discussing Matthew, below, I have no doubt that it was a village near the spot where Jesus landed.
Matthew clearly wrote ‘Gergesenes’ rather than ‘Gadarenes’. Since he was writing for a Jewish audience, and many Galileans would be quite familiar with the Sea of Galilee, he provided a more localized description. Further, try to picture the events in your mind. Do you suppose that the swineherds ran six miles to Gadara? The populace would certainly not run the six miles back. All of that would have taken entirely too long. To me it is obvious that there was a village close by, probably within half a mile, called ‘Gergesa’. It was to that village that the swineherds ran, told their story, and brought the residents back. Galileans familiar with the Sea of Galilee would certainly recognize ‘Gergesa’.
Not only does Matthew name a different place, he affirms that there were really two demonized men, whereas Mark and Luke mention only one. As a former tax collector, numerical precision was important to Matthew. Neither Mark nor Luke use the number ‘one’; they merely commented on the more prominent of the two, the one who wanted to go with Jesus. I understand that indeed there were two of them.
* 5: Although, as explained elsewhere, I understand that Matthew was published first, and Mark probably had a copy open before him as he wrote, yet he deliberately changed Matthew's ‘Gergesenes’ to ‘Gadarenes’—to his intended Roman audience ‘Gergesa’ would be unknown, while some would indeed know about ‘Gadara’.