Albert Barnes Commentary 1 Samuel 27:6

"Then Achish gave him Ziklag that day: wherefore Ziklag pertaineth unto the kings of Judah unto this day." — 1 Samuel 27:6 (ASV)

Ziklag - This was originally one of the cities of Simeon within the tribe of Judah (see marginal references), but it had been occupied by the Philistines. Its exact location is uncertain.

To this day - This phrase, coupled with the title "the kings of Judah," implies that this account was written after the revolt of Jeroboam and before the Babylonian captivity.