Chainat is one of the central provinces of Thailand. Neighboring provinces are (from north clockwise) Nakhon Sawan, Sing Buri, Suphan Buri and Uthai Thani.
Chai Nat is located in the flat river plain of central Thailand's Chao Phraya River valley. In the south of the province the Chao Phraya (formerly Chai Nat) Dam impounds the Chao Phraya river, both for flood control as well as to divert water into the country's largest irrigation system for the irrigation of rice paddies in the lower river valley. The dam, part of the Greater Chao Phraya Project, was finished in 1957 and was the first dam constructed in Thailand.