Seismic risk associated with the hilly and mountainous region of the Indian Himalayas is immensely high owing to a combination of the extremely high seismicity of the region and the vulnerability of the irregular buildings constructed on sloping terrain. Scientific studies on the seismic vulnerability of such buildings are performed on either bare frame or fully infilled buildings without considering openings in the infill panels for doors and windows. However, presence of openings plays an important role in the overall seismic performance. The present study aims to understand the effects of openings on the dynamic properties of unreinforced masonry (URM) infilled RC buildings constructed on sloping terrains such as the modal properties and fundamental period of vibration. Various opening ratios are considered as per construction practices in India, and the dynamic properties are compared with those of fully infilled buildings. A comparison of dynamic properties revealed that the period of vibration increases and the modal participation ratio corresponding to the fundamental mode of vibration decreases with an increase in the opening ratio. The displacement at the roof of the buildings was also found to increase with an increase in the opening ratio and the maximum displacement was found to be 25–63% higher as compared to fully infilled buildings depending on the opening ratio. Non-linear dynamic analysis has been performed to identify and compare key structural parameters responsible for the collapse of hill buildings with varying opening ratios.