In this study, we have investigated the relaxed domain structure of square-shaped ferromagnets by micromagnetic simulation. The simulation was performed to some basic ferromagnetic materials such as Cobalt (Co), Iron (Fe), Nickel (Ni), and Permalloy (Py). The side length of square-shaped ferromagnets was varied from 100 to 500 nm and the thickness were 5, 10, and 15 nm. The cell size was 2.5×2.5×2.5 nm3 and the damping factor α was 0.05. The initial magnetization state was random configuration. The domain structure was observed after the system reached equilibrium. We observed that there are two pattern of domain configuration, single domain (SD) and multi-domain (MD) structures. For all materials, the domain tended to form multi-domain structure as the side length and thickness increased. By analyzing the energy profiles, it was found that the SD structure exhibited the higher demagnetization energy than the exchange energy, while the MD structure showed the opposite.