The word here translated "plain" is applied in the rest of Scripture almost exclusively to the Ghor or Jordan valley. Compare, however, Nehemiah 12:28.

The priests, the men of the plain - Some of the officers of the temple, particularly the singers, dwelt in the plain country round about Jerusalem, Nehemiah 12:28; and it is likely that several of the priests dwelt in the same place.

And after him repaired the priests, the men of (e) the plain.
(e) Who dwelt in the plain country by Jordan and Jericho.

And after him repaired the priests, the men of the plain. Either of the plain of Jericho, where, in later times at least, there was a station of the priests, or of the plain about Jerusalem; those also assisted in the repairs of the wall.

Farther northwards repaired the priests, the men of the district of Jordan. כּכּר does not, as Bertheau infers from Nehemiah 12:28, signify the country round Jerusalem, but here, as there, the valley of the Jordan. See rem. on Nehemiah 12:28 and on Genesis 13:10. Hence this verse informs us that priests were then dwelling in the valley of the Jordan, probably in the neighbourhood of Jericho. The length of wall built by these priests is not further particularized.