BackgroundWhile loneliness is common in older adults, some immigrant groups are at higher risk. To inform tailored interventions, we identified factors associated with loneliness among immigrant and Canadian-born older adults living in Ontario, Canada.MethodsWe conducted a cross-sectional analysis of 2008/09 data from the Canadian Community Health Survey (Healthy Aging Cycle) and linked health administrative data for respondents 65 years and older residing in Ontario, Canada. Loneliness was measured using the Three-Item Loneliness Scale, with individuals categorized as ‘lonely’ if they had an overall score of 4 or greater. For immigrant and Canadian-born older adults, we developed separate multivariable logistic regression models to assess individual, relationship and community-level factors associated with loneliness.ResultsIn a sample of 968 immigrant and 1703 Canadian-born older adults, we found a high prevalence of loneliness (30.8% and 34.0%, respectively). Shared correlates of loneliness included low positive social interaction and wanting to participate more in social, recreational or group activities. In older immigrants, unique correlates included: widowhood, poor health (i.e., physical, mental and social well-being), less time in Canada, and lower neighborhood-level ethnic diversity and income. Among Canadian-born older adults, unique correlates were: female sex, poor mental health, weak sense of community belonging and living alone. Older immigrant females, compared to older immigrant males, had greater prevalence (39.1% vs. 21.9%) of loneliness.ConclusionsAlthough both groups had shared correlates of loneliness, community-level factors were more strongly associated with loneliness in immigrants. These findings enhance our understanding of loneliness and can inform policy and practice tailored to immigrants.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12877-023-04092-w.