The serpentinization of ultramafic rocks within the mantle wedge corner (MWC) of subduction zone forearcs plays a primordial role in geodynamic processes occurring at the intersection of the plate interface and the wedge corner. The MWC is also coincident with the occurrence of slow slip events in many subduction zones, including Cascadia. However, detailed constraints on the structural makeup of the MWC (e.g., geometry, percent serpentinization, fabrics, etc.) are lacking. We conduct receiver function (RF) analysis for 17 stations in northern Cascadia to characterize the subduction zone structure and the presence of seismic anisotropy in the MWC. We invert RFs for 1D shear-wave velocity (Vs) structure and identify the presence of a seismic low-velocity layer (LVL) marked by low Vs and high Vp/Vs for all stations in the analysis. We also observe a weak Moho within the overriding plate at shallower depth (25-35 km) than previous estimates. Observed seismic velocities in the MWC are compatible with ~5 km thick layer above the LVL containing 50%-100% serpentinites. We then use the results of the 1D inversion to solve for isotropic and anisotropic parameters of the MWC, including layer thickness, percent anisotropy, and symmetry-axis orientation. We confirm the ~5 km thick serpentinite layer, with ~14% anisotropy characterized by a slow axis of hexagonal symmetry. The symmetry axis corresponds with sub-horizontal foliations, consistent with fabric expected in sheared serpentinites. These results support layered serpentinization in the mantle wedge corner in Cascadia, with implications for fluid-mediated processes occurring near the MWC.