mainland north of Chiloé; the administrative center of the region is Puerto Montt.

Chiloé Island is by far the largest island in the archipelago, at 8394 km2. It is roughly rectangular, with its long axis oriented from north to south. To the east of Chiloé Island lies the Sea of Chiloé, which contains most of the other islands in the archipelago. The Sea of Chiloé is a marginal sea