While reading Colleen McCullough's The October Horse, I came across this passage (page 116):
In the southeast of the Delta lay the Land of Onias, an autonomous enclave of Jews descended from the High Priest Onias and his followers, who had been exiled from Judea for refusing to prostrate themselves flat on the ground before the King of Syria; that, Onias had said, they did only to their God. King Ptolemy VI Philometor gave the Onians a large tract of land as their own in return for an annual tribute and soldiers for the Egyptian army. The news of Cleopatra's generosity had spread to the Land of Onias, which declared for her in this civil war and made it possible for Mithridates of Pergamum to occupy Pelusium without a struggle; Pelusium was full of Jews and had strong ties to the Land of Onias, which was vital to all Egyptian Jews because it held the Great Temple. This was a smaller replica of King Solomon's temple, even to a tower eighty feet tall and artificial gulches to simulate the Vales of Kedron and Gehenna.
Intrigued by the idea of there having been another temple besides the one in Jerusalem, I did a bit of googling and came to the Jewish Encyclopedia (1901-1906) entry for Leontopolis, which gives Josephus as the source of our information about this temple.
Josephus was a Jewish historian who had fought on the Jewish side in the Jewish revolt against the Romans in the 60s AD, but then went over to the Roman side. He gives an account of Onias' founding of this Temple under Ptolemy Philometor (reigned 181 to 145 BC) in his "Antiquities of the Jews", though the correspondence between Onias and Ptolemy that Josephus quotes is probably not genuine -- Ptolemy seems remarkably well-informed about Judaism. Josephus gives a briefer account of the temple's founding and a note of its destruction by the Roman governors of Egypt after the Jewish revolt in his "The War Against the Jews" (the online Josephus passages are from the 18th century Whiston translation, but there are more modern translations in book form).
Those with access to .pdf files can read the 1906 report, with accompanying plates, of the excavations at Tell-al-Yahudiya (Arabic for Hill of the Jews), the site of Onias' temple, by the pioneering archaeologist, Flinders Petrie, who discusses Josephus' account of the temple and how it relates to what Petrie found.