Population: 535 (2001) 
Popularly, Telos was the son of Helios and Halia, the sister of the Telchines. He came to the island in search of herbs to heal his ill mother, and later returned to found a temple to Apollo and Neptune. However, Telos (Telo or Tilo) does not appear in Greek mythology and the name probably has an unknown pre-Hellenic origin.
Pliny the Elder notes that in antiquity Telos was known as Agathussa (Αγαθούσσα) (also Agathusa and Agathousa). In the middle ages it was known by the Italian Piscopi or Episcopi (also Pisconia).
Tílos has an inverted 'S' shape, is about 14.5 km long, north-west to south-east, with a maximum width of 8 km and an area of about 61 sq. km. The island has a mountainous limestone interior, volcanic lowlands, pumice beds and red lava sand, like its north western neighbour Nisyros. It is well supplied by springs, and is potentially very fertile and productive. Its coasts are generally rocky or pebbled, but there are also a number of sandy beaches.
At the north-west end of the island, the Monastery of Áyios Pandeleímon, (also the island's patron saint), sits on the slopes Mt. Profítis Ilías (651 m). The mountain borders a fertile plain running across the island's width, with the settlements of Áyios Andónis to the north and Éristos to the south. To the north-east of the plain is the island's capital, Megálo Chorió, built in the early 19th century at the foot of the ancient city of Telos. The archaic ruins strech up to the site of the acropolis of the ancient city, dedicated to Pythios Apollo and Poliada Athina, and the Venetian Kástro, built over it. To the west is Kharkhadió Cave, where excavations in 1971 unearthed Neolithic finds and bones of dwarf elephant. Above the cave stand the ruins of the medieval Fortress of Mesariá . At southern end of the island, bordered by more fertile meadows, is Livádhia, the major harbour and economic centre of the island. The island's old capital, Mikró Chorió, first settled in the 15th century by the Knights of the Order of St John, overlooks the bay. It has been completely abandoned since 1960, its inhabitants having moved down to the harbour in the 1930s. A number of other settlements such as Lethrá, Gherá & Panó Méri have similarly been abandoned. Mt. Áyios Nikoláos (367 m) stands to the south of the bay.
Kástros (castles) have protected the island's inhabitants from pirate raids since the dark ages.
- Megálo Chorió
- Mikró Chorió
- Stavroú Lámbrou
- Pottery and stone tools discovered in Kharkhadió indicate human activity on Tilos in the early neolithic period 8000 BC – 7000 BC, along with the large assembly of dwarf (1.20-1.60 m tall) elephant bones, carbon dated at 4000 – 7000 before present. Masseti (2001) suggests coexistence of these animals with humans, possibly into the historic period.
- Bronze Age
- Excavation has identified Pelasgian masonry, as well as suggesting Tilos was successively dominated by Minoans, Mycenaeans and Dorians.
- The island flourished during the classical era, minting its own coinage and being famed for clothing and perfumes.
- Telos claims the poetess Irinna (said to be Sappho's equal) was born on the island around 350 BC?. Charles Anthon (1853) describes her thus: "Erinna (Ήριννα) friend & contemporary of Sappho (about 612 BC) died at 19, left behind her poems which were thought worthy to rank with those of Homer. Her poems were of the epic class; the chief of them was entitled Ήλακάτη, " The Distaff" it consisted of three hundred lines, of which only four are extant. It was written in a dialect which was a mixture of the Doric and Æolic, and which was spoken at Rhodes, where, or in the adjacent island of Telos, Erinna was born. She is also called a Lesbian and a Mytilenean, on account of her residence in Lesbos with Sappho. There are several epigrams upon Erinna, in which her praise is celebrated, and her untimely death is lamented. Three epigrams in the Greek Anthology are ascribed to her, of which the first has the genuine air of antiquity, but the other two, addressed to Baucis, seem to be a later fabrication."
- In the 7th century BC, colonists from Tilos and Lindos settled in Sicily and founded the city of Gelas.
- Herodotus (484 BC – c. 425 BC) described the centuries preceding him as the golden age of Tilos.
- In the 5th century BC, Tilos was a member of the First Delian League and kept its independance until the end of the Peloponnesian War.
- From the turn of the 4th century BC, for the next 200 years, Tilos was subject to the Seleucid Empire, Caria and then Egypt under the influence of Rhodes, until in 200 BC, the island was incorporated in to the Rhodian confederacy.
- The island was conquered by the Romans in 42 BC. Archaeological finds from Roman and early-Christian times demonstrate the prosperity of the island until the great earthquake of 551 AD.
- Tilos followed Rhodes into the Byzantine Empire following the death of Theodosius I and was a member of the naval Theme of Samos between the 9th and 14th centuries.
- The Knights of St John took control of Tilos from 1309, restoring the Byzantine castles, and building new ones in order to defend against pirate raids, until 1522 when Rhodes fell to Suleiman I.
- In 1523, Tilos was occupied by the Ottoman Empire and the island was put under the privileged administrative and tax system known as "maktou". Christian pirates, under the pretext of revenge the against the Turks, pillaged the island constantly.
- 20th Century
- The Ottoman rule lasted until 1912, when the island was ceded to Italy. In 1943 it was invaded by German troops and in 1948, Tilos united with Greece, as did all the Dodecanese islands. Since 1948, the population of the island has declined rapidly, as many Tilians migrated to America or Australia.