Galatia was not a city, but a Roman province located in what is now northcentral and northeastern Turkey. It had earlier been overrun by Gauls, for whom the area was named, and was later incorporated in the Roman empire. Several of the cities reached on Paul's first missionary journey (Antioch of Pisidia, Iconium, Lystra, Derbe) were in the area just south of Galatia proper. They could be considered as Galatian churches, but there is no internal evidence to that effect. Possibly the churches Paul was writing to were certain unknown churches in Galatia proper, churches that Paul had reached on his second missionary journey.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8