Rapid urbanization and land scarcity obligated the urban population for multi-use of Reinforced Concrete (RC) buildings to meet both residential and commercial purposes together. Un-Reinforced Masonry (URM) infills are often placed irregularly in plan and or elevation of the buildings in some floor(s), particularly in the ground floor to suit the need of occupational requirements accompanied by the inherent irregularities due to openings for doors and windows to meet functional requirements for residence. Seismic performance of infilled frame highly depends upon degree of infill-frame interaction, and it is of utmost importance to classify infilled frame buildings in various Model Building Types (MBTs) based on the type of irregular placement of infills in addition to the parameters affecting seismic performance. Based on field pilot surveys carried out in Indian cities, URM infilled buildings have been classified into 14 different MBTs. Seismic performance of the prevalent categories of MBTs have been evaluated through Incremental Dynamic Analysis (IDA). It has been observed that irregular placement of infills increases the seismic collapse risk significantly, and reduces collapse capacity to approximately 50% as compared to ideal uniformly infilled building. Global collapse occurred due to failure of structural members in the vicinity of irregularity created due to infills.