Abstract We investigate the role of the elasticity and density of the forearc mantle wedge corner on the stress distribution in the forearc region of subduction zones, using numerical quasi‐2D lithospheric deformation models for the Cascadia, Nankai, NE Japan, and Costa Rica subduction zones. We incorporate the forearc mantle wedge corner as an elastic domain within the overriding lithosphere with physical properties that reflect reported degrees of serpentinization. In the models, we also incorporate reported values of effective friction coefficient (μ) and the downdip extent of frictional coupling (DoC) for the four subduction systems. Our models predict horizontal deviatoric tension in the wedge and the overriding crust in Cascadia and Nankai due to the buoyancy and elasticity of the wedge corner and relatively low DoC and μ. In NE Japan and Costa Rica, the plate coupling force dominates over the effect of the mantle wedge corner, resulting in horizontal deviatoric compression.