Củ Chi's name has nothing to do with steel or tunnels — it comes from a plant that once grew wild across this land, long before either of those associations existed.
"Củ Chi" is the folk name for a strychnine tree (mã tiền, Strychnos nux-vomica) that once grew abundantly in the area — the name became an official place name in 1956, centuries after the plant itself had already given the district its informal identity.
Villagers begin digging the first tunnel sections in the neighboring Phú Thọ Hòa area to the southeast, part of a wider pattern of underground resistance construction that will eventually spread across the whole region.
The tunnel network beneath Củ Chi is expanded into more than 200 kilometers of passages across three levels, the deepest reaching 8-10 meters underground — connecting villages, food stores, workshops, hospitals and command posts into a single continuous underground system.
In recognition of the district's role in the resistance, Củ Chi's soldiers and residents are awarded the title "Đất thép thành đồng" — "steel land, bronze wall" — a name that has stuck to the district ever since, alongside its more literal role as the tip of what American forces called the "Iron Triangle," together with Trảng Bàng in Tây Ninh and Bến Cát in Bình Dương.
The war leaves much of Củ Chi's farmland cratered and contaminated with unexploded ordnance; district authorities and residents begin the long process of clearing land and restoring agriculture.
Củ Chi district, previously split between Hậu Nghĩa province (Củ Chi district) and Bình Dương province (Phú Hòa district), is merged and placed under Ho Chi Minh City.
Củ Chi township is established from land cut out of Tân An Hội commune, giving the district its current structure of one township and twenty communes, a layout that has remained stable since.