CC Ādi 5.111

tāṅhā kṣīrodadhi-madhye ‘śvetadvīpa’ nāma
pālayitā viṣṇu, — tāṅra sei nija dhāma
Word for word: 
tāṅhā — within that; kṣīra-udadhi-madhye — in part of the ocean known as the ocean of milk; śvetadvīpa nāma — the island named Śvetadvīpa; pālayitā viṣṇu — the maintainer, Lord Viṣṇu; tāṅra — of Him; sei — that; nija dhāma — own residential quarters.
Translation: 
There, in part of the ocean of milk, lies Śvetadvīpa, the abode of the sustainer, Lord Viṣṇu.
Purport: 

In the Siddhānta-śiromaṇi, an astrological text, the different oceans are described as follows: (1) the ocean of salt water, (2) the ocean of milk, (3) the ocean of yogurt, (4) the ocean of clarified butter, (5) the ocean of sugarcane juice, (6) the ocean of liquor and (7) the ocean of sweet water. On the southern side of the ocean of salt water is the ocean of milk, where Lord Kṣīrodakaśāyī Viṣṇu resides. He is worshiped there by demigods like Brahmā.