Phachi is a community that grew from the establishment of the “Ban Phachi Junction Station,” a strategic transportation hub connecting the Northern and Northeastern regions of Thailand. Originally, the residents of Phachi lived sparsely scattered across the area. Later, during the reign of King Rama III (King Nangklao), there was a migration of Lao Wiang and Lao Isan people, which led to ethnic diversity and a multicultural society. Phachi is an area with access to the Pa Sak River. Its role as a railway junction significantly contributed to the town's growth. Furthermore, Phachi was involved in political events and was part of the railway transportation strategy after 1932 (B.E. 2475), exemplified by the Boworadet Rebellion, the Franco-Thai War (Indochina Dispute), and World War II
It can be assumed that from the late Ayutthaya period until the early Rattanakosin period before the reign of King Rama III, the area of Phachi was not inhabited by a settled community or permanent settlement. It might have been merely a grassland for raising horses used in warfare. Starting from the reign of King Rama III, following wars with the Laotian side, captives, specifically Lao Viang people from Vientiane and the Northeast (Isan) region, were relocated (or forcibly taken) to the area.
It is also assumed that the ancestors of the people of Phachi are the Lao Vientiane people who were forcibly relocated as war captives during the reign of King Rama III. This resulted in the Lao people being dispersed and settling from Nong Saeng District in Saraburi Province all the way to Tha Ruea District and the area of Phachi District in Phra Nakhon Si Ayutthaya Province.