Scanning microwave microscopy (SMM) allows nanoscale characterization of two-dimensional (2D) tin selenide (SnSe) polarization domain structure and resistance. This study examines SnSe flakes up to 15-nm thick, synthesized by low-pressure physical vapor deposition and transferred onto a silicon substrate. The SMM uncovers lateral polarization domains not detected by optical microscopy or atomic force microscopy. The SMM determines the resistivity of the domain interior is approximately 0.02 Ω·m, which is much higher than the resistivity of the domain boundaries. This observation agrees with current-voltage measurement of devices fabricated on 2D SnSe and vertical Piezoresponse Force Microscopy (PFM) measurement result. This work, in short, we report and confirm the domain boundary is more conductive than the domain interior both theoretically and experimentally demonstrates, plus SMM's efficacy for non-destructive, in situ monitoring of 2D materials and devices.