The following is the current list of provinces that have mask mandates in Thailand, which seems to increase on a daily basis.
Technically, the law applies to everywhere outside your home, including the beach and while driving your car or motorbike alone. There does not appear to be a clause for “exercise” as a caution to be an exception to wearing a mask.
Violations of the law could see you fined up to 20,000 baht (600 USD) under Thailand’s strict emergency decree laws to control the Covid-19 Coronavirus.
The list of provinces is:
Kanchanaburi (Technically only floating markets here), Prachinburi, Phetchaburi, Suphanburi, Ayutthaya, Samutsakorn, Lopburi, Samut Prakan, Prachuap Khiri Khan (Hua Hin), Chonburi (Pattaya), Saraburi, Trat (Including Koh Chang), Nonthaburi (Which also has a request to stay home from 9:00 P.M. to 4:00 P.M.), Surat Thani, Trang, Nakhon Si Thammarat, Narathiwat, Pattani, Phangnga, Phuket, Ranong, Satun, Songkhla, Yala, Sukhothai, Tak, Phetchabun, Uttaradit, Lamphun, Yasothon, Nong Khai, Ubon Ratchathani, Chaiyaphum, Mahasarakham, Mukdahan, Sisaket, Surin, Udon Thani, Loei, Amnat Charoen, Buriram, and Nakhon Phanom.
This list is increasing almost daily, this article may be updated as more provinces are added.