Objectives: To present the 12-month prevalence and correlates of suicidal ideation and attempts in a sample of youth in Ontario. Methods: Data come from the 2014 Ontario Child Health Study, a provincially representative survey of families with children in Ontario. Youth aged 14 to 17 y (n = 2,396) completed a computer-assisted, self-administered questionnaire in their home to assess the occurrence of suicidal ideation, suicidal attempts, and associated correlates, including non-suicidal self-injury, mental disorders, substance use, peer victimization and exposure to child maltreatment. Socio-demographic information was collected from the parent. Logistic regression models were used to identify correlates that distinguished between youth reporting: 1) no suicidal ideation or attempts, 2) suicidal ideation but no attempts, and 3) suicidal ideation and attempts. Results: The 12-month prevalence of suicidal ideation and attempts was 8.1% and 4.3%, respectively. All clinical and behavioural correlates were significantly higher among youth reporting suicidal ideation or attempts, as compared with non-suicidal youth. In adjusted models, depression and non-suicidal self-injury were each independently associated with elevated odds of suicidal ideation (OR = 4.84 and 4.19, respectively) and suicidal attempt (OR = 7.84 and 22.72, respectively). Among youth who reported suicidal ideation, the only variable that differentiated youth who attempted suicide v. those who did not, in adjusted models, was non-suicidal self-injury (OR = 3.89). Conclusions: Suicidal ideation and attempts are common among youth in Ontario, often co-occurring with mental disorders and high-risk behaviours. These findings underscore the need for effective prevention and intervention strategies, particularly for youth depression and non-suicidal self-injury.