The co-cathedral of Santa María la Mayor in Castellón de la Plana, also known as the Church of Santa María la Mayor, was a temple of Valencian Gothic style with later historicist interventions and neo-Gothic style. Its heritage significance was officially recognised when it was declared a National Historic-Artistic Monument in 1931.

On 24 July 1936, the temple suffered a serious fire. Months later, by municipal decision, it was demolished. The loss resulted in the disappearance of one of the most significant religious buildings in the capital of La Plana.

On 31 May 1960, a papal bull by Pope John XXIII created the new diocese of Segorbe-Castellón. From that moment on, the archpriestly church of Santa María de la Asunción in Castellón de la Plana—successor in functions of the original temple—was elevated to the status of co-cathedral, sharing cathedral rank with the see of Segorbe.