Diefflen has a catholic parish church: Saint Joseph and St. Wendelin. The first neo-gothic church of the architect Wilhelm Hector (1855–1918) was built in the years 1899-1900. After severe damage in World War II, the building was extensively extended in the years 1948-1950 according to the plans of the architects Alois Havener (Saarlouis) and Rudolf Güthler (Saarbrücken) and redesigned in the romanizing or late-antiquing abstraction-historicism.