Mizpah was built by Asa, 1 Kings 15:22, or rather enlarged or further built, for we read of it as a city belonging to the tribe of Benjamin, Joshua 18:26.
Related Commentaries of Jeremiah 40:6
Jeremiah 40:6
6 Then went Jeremiah unto Gedaliah the son of Ahikam to Mizpah; and dwelt with him among the people that were left in the land.