Saint-Pierre-de-Plesguen (Breton: Sant-Pêr-Plewenn) is a former commune in the Ille-et-Vilaine department in Brittany in northwestern France. On 1 January 2019, it was merged into the new commune Mesnil-Roc'h.

Hughes Felicité Robert de Lamennais lived in Saint-Pierre-de-Plesguen during the 19th century.

Inhabitants of Saint-Pierre-de-Plesguen are called saint-pierrais in French.

Historical population

Year Pop. ±% 1806 1,872 —     1826 2,050 +9.5% 1846 2,226 +8.6% 1866 2,507 +12.6% 1886 2,591 +3.4% 1906 2,619 +1.1% 1926 2,383 −9.0% 1946 2,287 −4.0%

Year Pop. ±% 1962 2,270 −0.7% 1968 2,164 −4.7% 1975 2,038 −5.8% 1982 2,023 −0.7% 1990 2,075 +2.6% 1999 1,977 −4.7% 2009 2,624 +32.7% 2022 3,072 +17.1%

• Communes of the Ille-et-Vilaine department

• Official website (in French)
• Cultural Heritage (in French)