EWTN Catholic Q&A
Why did Joseph and Mary go to Bethlehem?
Question from Curious George on 07-12-2012:

Luke chapter 2 tells us that Quirinius, the governor of Syria conducted a census of Judea upon assuming rulership. Josephus, Antiquities 18:14, tells us the same thing and that this was in 6 AD when Archelaus, ruler of Judea, King Herod's son and inheritor, was exiled after reigning ten years.

But Nazareth was in Galilee, not Judea,an it remained under the rulership of Herod Antipas, another of Herod's sons, until 37 AD.

Thus those living in Nazareth of Galilee were not counted in Quirinius' census.

So why would Mary and Jesus go to Bethlehem of Judea?

Answer by Fr. John Echert on 10-30-2012:

The requirement was to return to ones homeland, tribal area, and was not a census of those living in a particular location, as we do today

Father Echert