An unstructured electrostatic Particle-In-Cell Collisional (EUPICC) method is developed on arbitrary tetrahedral grids for simulation of partially ionized plasmas bounded by arbitrary geometries. EUPICC is parallelized and includes a multi-weight approach to address collisionless and collisional plasmas with arbitrary differences in species number densities. The electric potential is obtained from a finite volume multi point flux approximation of Gauss' law with Dirichlet, Neumann and external circuit boundary conditions. The matrix equation for the nodal potential is solved with a restarted generalized minimal residual method and a preconditioner algorithm. The electric field is obtained using the gradient theorem. EUPICC includes a real-collision-counter method for collision sampling of particles with arbitrary particle weights and a particle splitting-merge approach that incorporates spread in velocity space. Grid and temporal sensitivity analysis is performed, and the heating, slowing-down, and deflection times are evaluated. An extended set of simulations is performed for validation and verification and assessment of parallelization efficiency. EUPICC is applied to the simulation of a multi-species plasma flow over a nanosatellite and to ion beam neutralization.