Galilee was "the northern kingdom" of Israel though that kingdom was no longer God's people. The scattered sheep were referred to as "the lost sheep of the house of Israel" aka "Ephraim".
[Acts 2:7 NASB] (7) They were amazed and astonished, saying, "Why, are not all these who are speaking Galileans?
For more background please see my related answer.
Jesus said that he was sent only for the lost sheep of the house of Israel:
[Mat 15:24 ASV] (24) But he answered and said, I was not sent but unto the lost sheep of the house of Israel.
[Mat 10:5-6 ASV] (5) These twelve Jesus sent forth, and charged them, saying, Go not into any way of the Gentiles, and enter not into any city of the Samaritans: (6) but go rather to the lost sheep of the house of Israel.
The angel even refers to the disciples aka apostles as "You men from Galilee":
[Acts 1:11 CSB] (11) They said, "Men of Galilee, why do you stand looking up into heaven? This same Jesus, who has been taken from you into heaven, will come in the same way that you have seen him going into heaven."
For more background on the centrality of the recovery of the lost sheep to the theology of the NT I strongly recommend this video. I have it cued up to the meat and you can stop half way because after that it gets off base as far as I'm concerned.