Chiang Rai is the northernmost major city in Thailand, with a population of about 200,000 people. It is located in Mueang Chiang Rai District, Ch…Chiang Rai is the northernmost major city in Thailand, with a population of about 200,000 people. It is located in Mueang Chiang Rai District, Chiang Rai Province. Chiang Rai was established as a capital city in the reign of King Mangrai, in 1262 CE.