Measurement results and related analysis on the diffraction properties in the THz frequency band are reported. The results are given on the bands from approximately 100 GHz to 2 THz. Measurements were made for knife-edge diffraction, and diffraction through single and double slits. The diffraction effects are of interest in modeling the non-line-of-sight (NLOS) paths in the THz band. Therefore, the measurement results have significant practical value for designing the real communication systems. The theoretical models from the literature show a very good match to the measurement results. The key finding is that wireless communication links in the THz band can be established even in the shadows of the objects through diffraction with reasonable path loss. This also indicates another path in the THz multipath environment, as the previous studies have shown the THz radiation is capable on penetration, reflections, and scattering.