Acts 16:6 directly mentions Paul traveling through Galatia, the exact region where these churches were located.

Acts 18:23 records Paul strengthening disciples throughout Galatia again, linking directly to the churches addressed here.

1 Corinthians 16:1 refers to Paul's previous instructions to the Galatian churches, explicitly naming them as the same recipients.

In 1 Peter 1:1, Peter also writes to believers in Galatia, showing multiple apostles ministered to that region.