The Church of Santa María la Mayor is one of the two main medieval churches of Alcázar de San Juan, built in the late Gothic style in the 16th century. It stands in the old centre of town, its stone tower rising above the low surrounding buildings. The interior contains a notable main altarpiece from the early 17th century and some Baroque funerary sculpture.
The church is closely tied to the Cervantes controversy: one of the principal arguments that Alcázar de San Juan was the true birthplace of Miguel de Cervantes is a baptismal record from this church dating to 1558. Cervantes scholars have debated the matter for centuries — Alcalá de Henares claims the same honour with what most consider stronger evidence — but the town takes the claim seriously and the church is a starting point for the local Cervantes trail.