Nakhon Sawan, historically known as Muang Phra Bang, dates back to the Sukhothai era, serving as a strategic frontier city in military campaigns from the Sukhothai through the Rattanakosin periods. This region initially bore the name Chon Tawan, which later evolved into Nakhon Sawan or "City of Heaven" due to its auspicious connotations. Known widely as Pak Nam Pho, the name references its geographic importance where the Ping, Yom, and Nan rivers converge to form the Chao Phraya River, establishing the city as a central waterway junction. Some suggest the name Pak Nam Pho also alludes to the large Bodhi tree (or Pho) near the river's mouth, where today a shrine to Guan Yu stands.
During King Rama I’s reign, Nakhon Sawan served as a military base, reflecting its continued role in Thailand's defense against Burmese forces and northern rebellions. The city was classified as a third-level administrative town during King Ekathotsarot’s reign, underscoring its significant, though subsidiary, status in Thailand's historical governance structure. Nakhon Sawan’s strategic and cultural legacy endures, evidenced by historical military landmarks like the Khao Chong Khat pass, known for its role in past conflicts.