Nakhon Sawan is one of Thailand's seventy-six provinces (changwat). It lies in lower northern Thailand, neighbouring the provinces of Kamphaeng Phet, Phichit, Phetchabun, Lopburi, Sing Buri, Chai Nat, Uthai Thani, and Tak.

The provinces of Thailand are administrative divisions of the government of Thailand. The country is divided into 76 provinces proper, with one additional special administrative area. They are the primary local government units and act as juristic persons. They are divided into amphoe (districts) which are further divided into tambon, the next lower level of local government.