Hilchos Shemittah v’Yoveil 4:25

Shemittah is observed only in Israel, as per Leviticus 25:2: “When you come to the land....” Shemittah is observed whether or not the Temple is standing.

Hilchos Shemittah v’Yoveil 4:26

In the whole area acquired by the Jews who returned from Babylonia until K’ziv, it is prohibited to work the land during shemittah and the aftergrowth may not be eaten. In the whole area that was only acquired by the Jews who returned from Egypt – meaning from K’ziv to the river and to Mount Amana – one may not work the land during shemittah, but the aftergrowth may be eaten. Beyond the river and from the Mount Amana, one may work the land during shemittah.