Galatia was a district in the centre of Asia Minor, so called because it was settled by Gallic tribes in the 3rd Century BC.
Paul's letter to the Galatians has proved contentious, in that authorities don't agree on which cities were included in his epistle. One theory is that the Epistle was addressed to the people of Galatia Proper, situated in the centre of Asia Minor, towards the north. The other assumes that the Epistle was written soon after St. Paul's second visit to Derbe, Lystra, Iconium, etc. in the south of Galatia (Acts 16).
There is a fully-reasoned discussion of this controversy at Catholic Encyclopaedia. Perhaps the most telling argument in favor of the South Galatian theory is stated there as follows:
"The manner in which St. Paul mentions St. Barnabas in the Epistle indicates that the latter was known to those for whom the Epistle was primarily intended. St. Barnabas had visited South Galatia with St. Paul (Acts 13:14), but he was unknown in North Galatia."
On Paul's third journey he went over "all the country of Galatia and Phrygia in order" (Acts 18:23)
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Cities in Galatia
Below are links to the Galatian Churches most probably included in the Epistle to the Galatians: