Albert Barnes Commentary Matthew 3:5

"Then went out unto him Jerusalem, and all Judaea, and all the region round about the Jordan;" — Matthew 3:5 (ASV)

Jerusalem. The people of Jerusalem.

All Judea. Many people from Judea. It does not mean that literally all the people went, but that great multitudes went. It was general. Jerusalem was in the part of the country called Judea. Judea was situated on the west side of the Jordan. See Barnes on Matthew 2:1.

Region about Jordan. On the east and west side of the river; near to Jordan.