question: Health literacy is an essential social determinant of health and has been associated with positive health outcomes. While many sources of health information are widely available, people of different ages also have diverse social contexts and preferences for health information sources. This study aimed to identify health information sources and socio-demographics influencing health literacy in different social contexts across age groups: 15–29 years (young), 30–59 years (middle-age), and ≥60 years (elderly). We obtained secondary data from a cross-sectional study in northern Thailand from March to August 2019. Multivariate linear regression with age group subgroup analysis was used to determine factors associated with general health literacy by the Thai version of the health literacy questionnaire. Receiving health information from physicians was significantly associated with higher general health literacy in young (β 6.45, 95%CI 0.44–12.45; p = 0.035) and elderly (β 5.18, 95%CI 1.84–8.52; p = 0.002) groups, while receiving health information from health volunteers was significantly associated with a higher general health literacy in the middle-aged (β 2.89, 95%CI 0.38–5.39; p = 0.024) group. Although younger participants showed more frequent access to health information via the media than the other age groups, there were no media sources significantly linked with their general health literacy. Health information from physicians is a vital source of health information.