We report here single-layer ultracompact Fano-resonance photonic crystal membrane reflectors (MRs) at mid-infrared (IR) and far-IR (FIR) bands, based on single layer crystalline Si membranes. High-performance reflectors were designed for surface-normal incidence illumination with center operation wavelengths up to the 75- FIR spectral band. Large-area patterned MRs were also fabricated and transferred onto glass substrates based on membrane transfer processes. Close to 100% reflection was obtained at the spectral band, with a single-layer Si membrane thickness of 18 . Such Fano-resonance-based membranes reflectors offer great opportunities for high-performance ultracompact dielectric reflectors at IR and THz regions.