The municipality has a population of 5,834 (31 December 2024)[2] and it covers an area of 715.15 square kilometres (276.12 sq mi) of which 74.72 square kilometres (28.85 sq mi) is inland water (2018-01-01).

[1] The population density is 9 inhabitants per square kilometre (23/sq mi) (31 December 2024).

The first mention of a village named Tammela was in documents from 1423.

Neighbouring municipalities are Forssa, Hämeenlinna, Jokioinen, Karkkila, Lohja, Loppi, Somero and Urjala.

Hevoniemi, Hykkilä, Häiviä, Kallio, Kankainen, Kaukjärvi, Kaukola, Kuuslammi, Kytö, Letku, Liesjärvi, Lunkaa, Mustiala, Myllykylä, Ojainen, Pappila, Patamo, Pikonkorpi, Porras, Riihivalkama, Saari, Sukula, Susikas, Taljala, Talpia, Tammela, Teuro, Torajärvi, Torro.