Objectives The novel coronavirus outbreak required the population's compliance with public health measures yet young adults have been identified as having low risk perceptions and relatively low adherence with preventive measures. This study investigated third-level students' COVID-19 risk perception, knowledge and attitudes, and preventive behaviours between February and June 2021 to further understand young adults' beliefs and behavioural response to the COVID-19 pandemic in Ireland. Design Cross-sectional quantitative online survey design. Methods Three hundred and sixty-four university students completed an online survey which measured risk perception, preventive behaviours, knowledge of COVID-19, vaccination attitude and source of COVID-19 information. Results University students in Ireland reported high levels of knowledge of COVID-19 and high adherence to preventive behaviours. While risk perception levels were moderately high, students displayed higher concern for others than for themselves. High levels of risk perception significantly predicted preventive behaviours while general knowledge of the virus increased the likelihood of vaccine uptake. Over two-thirds of participants were willing to take the COVID-19 vaccine if available. Conclusions Vaccination hesitancy remains a concern among the young adult population requiring urgent attention from public health officials. The implication for health policymakers is that positive behavioural responses of the young population can be reinforced by targeting risk perceptions and by increasing the public's knowledge and understanding of COVID-19.