Nanocrystalline ferrihydrite (bulk formula 5Fe2O3.9H2O) synthesized by hydrolysis of Fe(III) nitrate at 348K was investigated by neutron diffraction at 5, 293 and 323K. The structure is refined as a sum of a defect-free phase (space group P 1c) and a defective phase (space group P3) based on earlier discussed models from X-ray diffraction results on a six-line ferrihydrite. The size of the nanoparticles was found to be 2.7(0.8)nm. The material reveals antiferromagnetic order below TN=330(20)K with collinear Fe spins (sequence +-+-) perpendicular to the trigonal axis. The ordered moment is 3.2μB/Fe at 5K.