The first group of Jews to leave Babylon for Judah arrived about 537, under the leadership of "Sheshbazzar the Prince of Judah" (Ezra 1:8).  The identity of this person is a matter of much dispute, with very little historical grounding to base it on.  Some older scholars (Josephus’ Antiquities)  believed him to be the same person as Zerubbabel (Ezra 2:2), but this is now deemed unlikely (NIV, p 673 FN).  Zerubbabel ("offspring of Babylon") a descendant of David, and of the last king of Judah (NIV, p. 680), was one of the non-priestly leaders of the returned community.

        

The Book of Ezra even provides the numbers of returning exiles, and their families, and the numbers of mules and camels! (Ezra 2).  This total is also given in Nehemiah 7.  The problem for scholars is that the sum of all the families listed doesn't equal the grand total of 42,360.  We will let them enjoy themselves with their calculators and arguments.  The significant point is that about 50,000 people returned to Judah at this time, which is a significant force, large enough to upset the population balance back in Judah -- yet not nearly the majority of the Jews in Babylon (NIC, p.11).  At this time, the former kingdom of Israel was inhabited by relocated prisoners of war of the Assyrians, while Judah contained Babylonian transplants and the offspring of non-exiled citizens of Judah and Benjamin.

        

Note here the selective purpose of God at work.   He didn't draft people to rebuild His Temple.  Those who were happy and prosperous in their exiled locality either emigrated in the next century or became part of a large Jewish Diaspora in the Near East: putting down roots in India and the "stan" countries (Pakistan, Afghanistan, Turkmenistan, etc).  We can assume that the people who joined Sheshbazzar on a 500-mile trek to a homeland most of them had never seen were the "true believers."  They were zealous not only to build the Temple but to restore the religious covenant that was the unique possession of Israel.  This was the righteous remnant foretold by the prophets:

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          In that day the Lord will reach out his hand a second time to reclaim the remnant that is left of his people from Assyria, from Lower Egypt, from Upper Egypt, from Cush, from Elam, from Babylonia, from Hamath and from the islands of the sea (Isa 11:11).

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          Once more a remnant of the house of Judah will take root below and bear fruit above (Isa 37:31).

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          But the significant characteristic of this remnant is that it was self-chosen.  These were the true children of Abraham, who resembled him in their spirit of adventurous faith, and who copied his journey more than 1000 years later.

         

Upon arrival, most of the people did not settle in Jerusalem, but went to their ancestral towns (Ezra 2:70).  It has been suggested that the reading of the Septuagint is more accurate here -- the priests, Levites and temple workers settled in Jerusalem, and the rest of the people elsewhere (NIC, p. 58).  
    
We also note the problem of people who could not prove their heritage:  Ezra 2:59-63.  The disruptions of conquest and exile may very well have destroyed certain family genealogical records.  These records became very important in the re-establishment of a pure religious community in Jerusalem.  Men who could not prove their descent were excluded from the priesthood until a discernment of the will of God could be made by use of the Urim and Thummim.