Greco-Roman name for the land of the tribe of Judah, whose only stable border was fixed by the Dead Sea to the east. The tribal homeland had about a fifteen mile radius in the hill country of the southeastern corner of Palestine, with its center at Hebron. There mountain ridges rose to almost 3400 feet above the level of the Mediterranean only to descend 4,700 feet eastward to the surface of the Dead Sea, the lowest spot on the face of this planet.
David's conquest of Jerusalem on the border with Benjamin shifted Judea's center further north. During the reigns of David and Solomon [10th c. BCE] the tribe of Judah absorbed the ancestral lands of Benjamin (to the north of Jerusalem), Dan (to the west) and Simeon (to the south). So after Solomon the northern boundary of Judah ran on a line just north of Modein in the west to Jericho in the east. After the Babylonian exile [6th c. BCE], the province of Judea was reduced to a ring of about a 10 mile radius around Jerusalem.
After Judea won independence from Hellenistic Syria [2nd c. BCE], Judah Maccabee's brother Jonathan extended its borders westward to the Mediterranean from Joppa to Gaza and John Hyrcanus annexed the historic Judean homeland in the south that had been claimed by Idumea. Though later Hasmoneans extended Judean control over Samaria, Perea, Galilee and the Golan, these were treated as occupied territories and never integrated into Judea even under Herod. So, except for Samaria these territories were easily separated from Judea after Herod's death. During the 1st c. CE the Roman province of Judea proper was about 45 miles square.
Sources: Into His Own