Guillemundus (also Guillemó) (died 827) was count of Razès and Conflent, in what is now southern France.
He was son of Bera of Barcelona. He received these counties from delegation of his father (before 820) and retained them when Bera died in 820. In 826 he joined the revolt of Aysun or Aissó and, routed, fled to Córdoba.
The name Guillemundus was given him in honour of his great father William (Guillem) the Saint, count of Toulouse, cousin of Charlemagne, but with the ending "undus" probably by the influence of William's wife Cunegunda.