Background and aim: Streptococci, mainly mutans streptococci, are known as the causative microbes of dental caries, but there is limited clarity about their impact on the tooth level and the distribution of streptococci species in different dentition stages. This study evaluates the distribution of streptococci species in primary and permanent teeth in children and adolescents with caries. Materials and methods: The study population consisted of two groups: subjects with caries in primary teeth aged 2–5 years and adolescents with caries in permanent teeth aged 12–15 years. Age-matched controls were included in both groups. The decayed, missing, and filled teeth for primary teeth/decayed, missing, and filled teeth for permanent teeth (dmft/DMFT) index score was recorded according to World Health Organization (WHO) protocol. Dental biofilm samples were obtained from tooth sites under sterile conditions and placed in sterile transport media. Inoculation was performed on specific media, colonies were counted, and streptococci species were identified. Results: In subjects with primary dentition caries, the streptococci species identified were Streptococcus mutans (S. mutans), S. sobrinus, S. mitis, S. rattus, and S. sanguis. In subjects with caries in permanent teeth, S. salivarius, Enterococcus faecalis (E. faecalis), S. mitis, and S. agnosus were seen in addition to S. mutans and S. sobrinus. The levels of mutans streptococci colony-forming units (CFU) were significantly higher in the primary caries group in children (p < 0.01). However, the CFU of streptococci in the healthy control group in children was not statistically different from the CFU/mL of streptococci in the healthy control group in adolescents. Conclusion: A significant difference (p < 0.01) in the streptococci species profile was observed between primary and permanent teeth with caries.