The 21 provinces where these sites are located are: Chiang Mai, Mae Hong Son, Nan, Tak, Phitsanulok, Uthai Thani, Lampang, Lamphun, Nakhon Sawan, Uttaradit, Phetchabun, Bangkok, Ayutthaya, Ratchaburi, Phetchaburi, Prachuab Khiri Khan, Kanchanaburi, Suphanburi, Lopburi, Saraburi and Chonburi.
Among the famous attractions that have been closed are: Huai Nam Dang National Park in Chiang Mai (until April 30), Si Nan National Park in Nan (until June 30), Umphang Wildlife Sanctuary in Tak (until April 30), Chae Son National Park in Lampang (until further notice) and The Grand Palace and Temple of the Emerald Buddha in Bangkok (until further notice).
The full list can be viewed here: https://www.tatnewsthai.org/news_detail.php?newsID=5057