We study the ground state and magnetic hysteresis properties of 2d arrays (L x × L y ) of dipolar interacting magnetic nanoparticles (MNPs) by performing micromagnetic simulations. Our primary interest is to understand the effect of sample shape, Θ-the ratio of the dipolar strength to the anisotropy strength, and the direction of the applied field H = H o êH on the ground state and the magnetic hysteresis in an array of MNPs. To study the effect of shape of the sample, we have varied the aspect ratio A r = L y /L x which in turn, is found to induce shape anisotropy in the system. Our main observations are: (a) When the dipolar interaction is strong (Θ > 1), the ground state morphology has in-plane ordering of magnetic moments. (b) The ground state morphology has randomly oriented magnetic moments which is robust with respect to system sizes and A r for weakly interacting MNPs (Θ < 1). (c) Micromagnetic simulations suggests that the dipolar interaction decreases the coercive field H c . (d) The remanence magnetization M r is found to be strongly dependent not only on the strength of dipolar interaction but also on the shape of the sample. (e) Due to anisotropic nature of dipolar interaction, a strong effect of shape anisotropy is observed when the field is applied along longer axis of the sample. The dipolar interaction in such a case induces an effective ferromagnetic coupling when the aspect ratio is very large. These results are of vital importance in high-density recording systems, magneto-impedance sensors, etc.