The Co-cathedral of Santa María, also known as the church of Santa María la Mayor in Castellón de la Plana (Spain) is a temple in the Valencian Gothic style with later historicist and neo-Gothic interventions. It is located in the Plaza Mayor, next to the Town Hall and the free-standing bell tower known as El Fadrí.

The construction of the temple began in the 12th century. Destroyed by a fire, work was resumed in the mid-14th century, being extended at the beginning of the 15th century by the master builder Miguel García de Segorbe, and the church was consecrated in 1549.

It had a single nave divided into five bays, a pentagonal apse with two side chapels and a central one for the choir, as well as chapels between the buttresses, covered with ribbed vaults over the bays and a star-shaped vault over the apse.

The church had three doorways: two lateral ones, located in the third bay of the nave, and another one on the main façade, which, together with some keystones, are the only elements preserved in its reconstruction.

In 1662, with traces by Juan Ibáñez, the Communion chapel was built with a Greek cross plan and covered with a dome in the centre and half-barrel vaults on the arms, which opened in the foot section of the Epistle side.

The Co-cathedral of Santa María, declared a National Historic-Artistic Monument in 1931, was deliberately set on fire on 24 July 1936 in the early days of the Civil War and demolished months later by municipal agreement. Its reconstruction, begun in 1939 on the basis of a project by Vicente Traver Tomás based on the traces of the disappeared temple, was completed in 1999.

The current church, which occupies an entire block, has a Latin cross plan with three naves and a pentagonal apse. The central nave is highlighted by octagonal pillars, from which the transverse arches start. The naves are covered with ribbed vaulting, the chevet being half star-shaped, and the transept, with a dome, is also covered with star-shaped vaulting.