John Gill Commentary 1 Chronicles 9

So all Israel were reckoned by genealogies
Not now by the writer of this book in the preceding chapters; for two of the tribes are not reckoned at all, and the rest but in part; but there had been kept an exact account of them:

and, behold, they were written in the book of the kings of Israel ;
not in the canonical book or books of Kings, but in the annals, journals, and diaries, which each king took care to be kept with some exactness, often referred to in the preceding books; out of which this writer, under a divine direction, had taken what was proper to be continued, and had carried the genealogy down to the captivity of the ten tribes; but the genealogy being lost with them, he could proceed no further, nor say anything more concerning them:

but Judah ;
for so the word should be stopped, and read according to the Hebrew accents:

[who] were carried away to Babylon for their transgression ;
their idolatry, and were now returned again; of them the writer proposes to give a further account.

Now the first inhabitants that dwelt in their possessions in
their cities
Who first returned from Babylon upon the proclamation of Cyrus, and enjoyed their former possessions, and dwelt in the cities they had before, or in such as were allotted them, or they chose:

[were], the Israelites, the priests, Levites, and the Nethinims ;
the whole body that returned were divided into four classes, as they had been before the captivity; the Israelites were the common people in general, the body politic; the priests, the ecclesiastics, who officiated in sacred things; the Levites, who ministered to them; and the Nethinims were such persons as were "given", as the word signifies, to do servile work for the sanctuary, as, to be hewers of wood and drawers of water; such were the Gibeonites, (Joshua 9:27) , and such as were appointed by David for such work, see (Ezra 8:20) .

And in Jerusalem dwelt of the children of Judah, and of the
children of Benjamin
Of which tribes were the largest number that went into, and returned out of, captivity:

and of the children of Ephraim and Manasseh ;
such of those tribes who had joined the others when Jeroboam introduced his idolatry, or had fled to them when Samaria was besieged and taken by Shalmaneser, and so went into captivity with Judah, and now returned; and as many of them as took the advantage of the proclamation of Cyrus, who were carried captive with the ten tribes.

Uthai, the son of Ammihud
Called Athaiah, (Nehemiah 11:4) though his ancestors there are differently reckoned here; his genealogy here is traced from his father Ammihud, through Omri, Imri, Bani, Pharez, to Judah.

And of the Shilonites
Not called so from the city of Shiloh, which was in Ephraim; whereas these here intended were of the tribe of Judah, and were either the descendants of a man whose name was Shiloni, (Nehemiah 11:5) or rather these are the same with the Shelanites, (Numbers 26:20) so called from Shelah the son of Judah; and so the Targum here is, ``and of the tribe of Shelah:'' Asaiah the firstborn, and his sons ;
the same with Maaseiah, (Nehemiah 11:5) .