Boyd’s Bible Dictionary:

(circle). Originally the circuit containing the 20 towns given by Solomon to Hiram (Josh. 20:7; 1 Kings 9:11; 2 Kings 15:29). In time of Christ, one of the largest provinces of Palestine, in which he spent the greater part of his life and ministry (Luke 13:1; 23:6; John 1:43-47; Acts 1:11).

Concise Bible Dictionary:

This was a much smaller district in the Old Testament than in the New Testament, although its area is not very defined. It seems formerly to have included a portion of Naphtali, and perhaps a portion of Asher. “Kedesh in Galilee,” one of the cities of refuge, was in Naphtali (Josh. 20:7; Josh. 21:32; 1 Chron. 6:76). Solomon gave Hiram twenty cities in Galilee. These are not named, but they would naturally be near to Tyre. When Hiram went to view them he called them the “land of Cabul,” as if he included them all under the one name of “Cabul,” worthless. Now there was and is a village of this name on the frontier of Asher, which would seem to indicate that Asher was in the district of Galilee (1 Kings 9:11-13). About B.C. 740 Tiglath-pileser carried away captive all the inhabitants of Naphtali, &c. (2 Kings 15:29). This was doubtless followed by the district being inhabited by foreigners, who, when the captivity of Israel was completed, would be able to spread themselves southward. Hence the term “Galilee of the Gentiles” or nations, which does not occur until Isaiah 9:1: the prophecy is quoted in Matthew 4:15.
In New Testament times Galilee had become a much larger district, including the portions of Asher, Naphtali, Zebulon, and Issachar. It had over 200 towns and villages, and about three million inhabitants in Josephus’ time. It was bounded on the south by Samaria, and embraced the whole of the north part of Palestine. It included the towns of Nain, Nazareth, Cana, Tiberias, Magdala, Dalmanutha, Bethsaida, Chorazin, and Capernaum.
It is probable that the Galilaeans had a different manner of pronunciation, or the language spoken in Galilee was not so refined as that spoken at Jerusalem, which led to Peter being detected by his speech (Matt. 26:69, 73; Mark 14:70). But the voice of the same Peter, under the power of God, was mighty on the day of Pentecost, though the hearers said “are not all these which speak Galilaeans?” (Acts 2:7). They were surprised to hear such men speak in foreign tongues, the more so because no prophet was ever looked for from thence, nor any good thing from Nazareth (John 1:46; John 7:52). Still in that despised district the Lord spent His youth: thus early was He as One separated from the course of the nation of Israel, a Nazarene; and the principal part of His ministry was among the poor of the flock in that locality; fulfilling thus the will of God and the prophetic word, on which God had caused His people to hope.