The municipal unit Vilia covers the mountainous northwestern part of Attica, and has a land area of 144.851 km². The main mountain ranges are Kithaironas (1,409 m) in the northwest and Pastra in the northeast. In the west it stretches along the coast of the Alkyonides Gulf, a bay of the Gulf of Corinth. The village Vilia, the largest in the municipal unit, lies in the easternmost part, at the southeastern foot of Kithaironas. Vilia is 6 km south of Erythres, 7 km west of Oinoi, 10 km east of the coastal village Aigosthena, 17 km south of Thebes and 40 km northwest of Athens.
The municipal unit's largest villages are Vilia (pop. 1,269 in 2011), Kato Alepochori (220), Aigosthena (80), Veniza (52), and Agios Nektarios (40).