Montaillou ([mɔ̃.ta.ju]; Occitan: Montalhon) is a commune in the Ariège department in the south of France.

Its original, medieval location was abandoned and the current village is a short distance away.

When Fournier became Pope he took the records of the investigation with him and they remain in the Vatican Library.

[3] In medieval times, the old village was guarded by the Château de Montaillou, now a ruin.

The village church, dedicated to Notre Dame de Carnesses, remains in use.