The aim of this study is to obtain knowledge about which cultivable bacterial species are present in indoor air in homes, and whether the concentration and species composition of airborne bacteria is associated with different factors. Measurements have been performed for one whole year inside different rooms in 5 homes and once in 52 homes. Within homes, a room-to-room variation for concentrations of airborne bacteria was found, but an overlap in bacterial species was found across rooms. Eleven species were found very commonly and included: Acinetobacter lowffii, Bacillus megaterium, B. pumilus, Kocuria carniphila, K. palustris, K. rhizophila, Micrococcus flavus, M. luteus, Moraxella osloensis, and Paracoccus yeei. The concentrations of gram-negative bacteria in general and the species P. yeei were significantly associated with the season with highest concentrations in spring. The concentrations of P. yeei, K. rhizophila, and B. pumilus were associated positively with relative humidity, and concentrations of K. rhizophila were associated negatively with temperature and air change rate. Micrococcus flavus concentrations were associated negatively with air change rate. Overall, this study identified species which are commonly present in indoor air in homes, and that the concentrations of some species were associated with the factors: season, air change rate, and relative humidity.