Abstract Background Loneliness can affect up to 30% of older adults and is associated with increased morbidity and all cause mortality. Loneliness is also a major risk factor for depression. We aimed to explore the predictors of loneliness in older Irish adults and its relationship to depression. Methods Study participants were Irish adults aged >60 years in the Trinity Ulster University Department of Agriculture (TUDA) study. Participants with an MMSE <24 were excluded, to prevent the inclusion of individuals with dementia. Loneliness in the last week was identified from the 'loneliness' question in the Center for Epidemiological Studies Depression Scale (CES-D) and considered present when experienced ≥1-2 days in the last week and absent when experienced rarely or none of the time. Depression was defined as a CES-D ≥16. Predictors of loneliness were explored in multinomial regression models as well as its association with depression. Results There were 4561 participants, 70% female, mean age 70.1 years and 21.6% experienced loneliness. Positive independent predictors of loneliness were living alone (OR 5.2, CI 4.41-6.14, p<0.001), female sex (OR 1.29, CI 1.07-1.56, p=0.009), timed up and go >12 seconds (OR 1.46-2.32, p<0.001) non-driving status (OR 1.37, CI 1.13-1.67, P=0.001) and lower MMSE (OR 0.57, CI 0.41-0.79, p=0.0006). Those who reported loneliness had a higher prevalence of depression (32.1 vs 3.3%, p<0.0001). Conclusion Living alone was, as expected, the greatest predictor of loneliness followed by physical frailty, non-driving status, female sex, and lower cognition. A high proportion (one third) who felt lonely had depression, though low mood may increase the perception of loneliness independent of social engagement. A limitation is that we did not have a specific validated tool to assess loneliness or to distinguish between `emotional' or `social' loneliness.