Of the three returnees, one patient, aged 38, had arrived from Austria and two, aged 26 and 38, had returned from Hong Kong. All the Thai nationals were female.
The domestic case was a 57-year-old French tourist, who visited Koh Samui in Surat Thani province with her husband and son.
Koh Samui Hospital showed a positive result on October 21, and the result was again confirmed by the Regional Medical Sciences Centre 11 in Surat Thani on October 22.
However, her husband and son have tested negative. Further information on the French tourist can be checked here.
As of Saturday, the number of confirmed cases in Thailand increased to 3,731 (783 in state quarantine), 143 are in hospital, 3,529 have recovered and been discharged and 59 have died.
According to Worldometer, as of 9am on Friday, the number of confirmed global cases had risen to 42.46 million, 31.42 million have recovered, 76,477 are in serious condition and 1.14 million have died.
Thailand ranks 146th for most cases in the world.
The US has the most number, with 8.74 million, followed by India (7.81 million), Brazil (5.35 million), Russia (1.48 million) and Spain (1.11 million).