The Archipelago Sea is a part of the Baltic Sea between the Gulf of Bothnia, the Gulf of Finland and the Sea of Åland, within Finnish territorial waters. By some definitions, it contains the largest archipelago in the world by the number of islands, estimated at 50,000, although many of the islands are very small and tightly clustered.

The larger islands are inhabited and connected by ferries and bridges. Åland, including the largest islands of the region, forms an autonomous region within Finland. The rest of the islands are part of the region of Southwest Finland. The Archipelago Sea is a significant tourist destination.

The Archipelago Sea covers a roughly triangular area with the cities of Mariehamn, Uusikaupunki, and Hanko at the corners. The archipelago can be divided into inner and outer archipelagos, with the outer archipelago consisting mainly of smaller, uninhabited islands. The total surface area is 8,300 square kilometres (3,205 square miles), of which 2,000 square kilometres is land.

The archipelago has a vast number of islands. The exact number depends on the definition of the term "island", as the size of the patches of dry land in the area varies from small rocks peeking out of the water to large islands with several villages or even small towns. The number of the larger islands of over 1 square kilometre (0.4 sq mi) within the Archipelago Sea (in provinces of Åland Isles and Southwest Finland) is 257, whilst the number of smaller isles of over 0.5 hectares (1.2 acres) is about 17,700.

If the number of smallest uninhabitable rocks and skerries is accounted for, 50,000 is probably a good estimate. 36,563 islands make up the Canadian Arctic Archipelago, in contrast. Indonesia has 17,508 islands, according to the Indonesian Naval Hydro-Oceanographic Office. The Philippines has 7,641 islands.

According to en.wikipedia.org