  SOFIA/HAWC+ 154 $\mu$m Far-Infrared polarimetry observations of the
well-studied edge-on galaxy NGC 891 are analyzed and compared to simple disk
models with ordered (planar) and turbulent magnetic fields. The overall low
magnitude and the narrow dispersion of fractional polarization observed in the
disk require significant turbulence and a large number of turbulent
decorrelation cells along the line-of-sight through the plane. Higher surface
brightness regions along the major axis to either side of the nucleus show a
further reduction in polarization and are consistent with a view tangent to a
spiral feature in our disk models. The nucleus also has a similar low
polarization, and this is inconsistent with our model spiral galaxy where the
ordered magnetic field component would be nearly perpendicular to the
line-of-sight through the nucleus on an edge-on view. A model with a barred
spiral morphology with a magnetic field geometry derived from radio synchrotron
observations of face-on barred spirals fits the data much better. There is
clear evidence for a vertical field extending into the halo from one location
in the disk coincident with a polarization null point seen in near-infrared
polarimetry, probably due to a blowout caused by star formation. Although our
observations were capable of detecting a vertical magnetic field geometry
elsewhere in the halo, no clear signature was found. A reduced polarization due
to a mix of planar and vertical fields in the dusty regions of the halo best
explains our observations, but unusually significant turbulence cannot be ruled
out.
