Ionian Greeks

Who the Ionians were and whence they came to Greece is not entirely certain. Solon, Herodotus, and Homer (as well as Pherecydes) believed they originated on the mainland in central Greece. The Athenians considered themselves Ionian, though the Attic dialect is somewhat different from that of the cities of Asia Minor. Tisamenus, grandson of Agamemnon, evicted from the Argolid by Dorians, drove the Ionians from the Northern Peloponnese into Attica, after which time that district was known as Achaea. More Ionian refugees arrived in Attica when the Heracleidai drove Nestor's descendants from Pylos. The Neleid Melanthus became king of Athens, as did his son Codrus. (And hostilities between Athens and Boiotia date back at least to 1170 B.C. if we accept Thucydides' dates.)

Neleus, son of Codrus, was one of the leaders of the Ionian migration to Asia Minor, and was thought to have founded (re-founded) Miletus. Along the way his followers and sons occupied Naxos and Mykonos, driving the Carians out of the Cycladic islands. Neleus' brother Androclus, known to Pherecydes as the instigator of the migration, drove the Lelegians and the Lydians out of Ephesus and founded the archaic city and the cult of Artemis. He found himself at odds with Leogrus of Epidaurus, king of Samos. Aepetus, one of the sons of Neleus, founded Priene, which had a strong Boeotian element in its population. And so on for each city. Not all were settled by Ionians from Attica: some settlements were Pylian, some from Euboea.

The above is from the notes of Sallie Goetsch of Didaskalia.

Primary Sources and Select Passages:
Strabo 14.1.7 - Milesians.
Herodotus Histories Book I:
Greek Races
Herodotus Histories Book I.56. By these lines when they came to him Crœsus was pleased more than by all the rest, for he supposed that a mule would never be ruler of the Medes instead of a man, and accordingly that he himself and his heirs would never cease from their rule. Then after this he gave thought to inquire which people of the Hellenes he should esteem the most powerful and gain over to himself as friends. And inquiring he found that the Lacedemonians and the Athenians had the pre-eminence, the first of the Dorian and the others of the Ionian race. For these were the most eminent races in ancient time, the second being a Pelasgian and the first a Hellenic race: and the one never migrated from its place in any direction, while the other was very exceedingly given to wanderings; for in the reign of Deucalion this race dwelt in Pthiotis, and in the time of Doros the son of Hellen in the land lying below Ossa and Olympos, which is called Histiaiotis; and when it was driven from Histiaiotis by the sons of Cadmos, it dwelt in Pindos and was called Makednian; and thence it moved afterwards to Dryopis, and from Dryopis it came finally to Peloponnesus, and began to be called Dorian.

Ionians

Herodotus Histories Book I.142. These Ionians to whom belongs the Panionion had the fortune to build their cities in the most favourable position for climate and seasons of any men whom we know: for neither the regions above Ionia nor those below, neither those towards the East nor those towards the West.

12 Cities

Herodotus Histories Book I.145. Upon these they laid this penalty: but as for the Ionians, I think that the reason why they made of themselves twelve cities and would not receive any more into their body, was because when they dwelt in Peloponnesus there were of them twelve divisions, just as now there are twelve divisions of the Achaians who drove the Ionians out: for first, (beginning from the side of Sikyon) comes Pellene, then Aigeira and Aigai, in which last is the river Crathis with a perpetual flow (whence the river of the same name in Italy received its name), and Bura and Helike, to which the Ionians fled for refuge when they were worsted by the Achaians in fight, and Aigion and Rhypes and Patreis and Phareis and Olenos, where is the great river Peiros, and Dyme and Tritaieis, of which the last alone has an inland position.

Next: Homeric Geography