Access, effectiveness, and utilization of healthcare services can affect the attainment of good health as healthcare services have a role in promoting the population's health and livelihoods of communities. Understanding factors that drive an individual's preference in seeking health care from a particular source(s) is an important aspect that has a profound contribution in facilitating the effective provision of health services. Though this aspect is generally known; very scanty information is available on what drives individuals’ preference on health care service sources under One Health Approach in Tanzania. A cross-sectional study was conducted in Morogoro municipality and Mvomero district in Tanzania, inter alia, to analyse the determinants of individuals' health care service source preference. A structured questionnaire administered through a Computer-Aided Personal Interviewing (CAPI) electronic platform was used to collect data from 1440 respondents obtained through a multistage sampling procedure. IBM-SPSS v20 was used to analyse quantitative data. Binary logistic regression determined an individual preference for sources to seek health care. The results revealed that 41.2% of the respondents preferred to seek health care services from informal sources and 58.8% from formal sources. Marital status (Exp B= 0.001, 95% CI, .000 to .010), ß=-6.946, p=0.000, service characteristics (Exp B= 1.678, ß=0.518, p=0.000), beliefs on the effectiveness of health services (Exp B= 5.268, ß=1.662 at p=0.001) had significant influence on determining preference for a source of health care. It is recommended that health services should be improved from the formal health care sources since the majority of respondents had a preference for it