Background As both lifetime and daily use of marijuana remain prevalent among US adolescents and are likely to increase, given the legalisation of marijuana in a number of states, their correlates with other negative (including delinquent) behaviours have been studied. Most of this research has been carried out with general‐population‐based samples. Thus, little is known about this association among court‐involved and detained juveniles. Aims This study aimed to assess lifetime and daily marijuana use among detainees aged 10–16 years. Our hypotheses were that such use would be higher among youth who had been in detention than in general population samples and that it would be associated with other mental health indicators and criminal justice indicators, such as total number of detentions and number and types of charges. Methods The records of a random 20% sample of all juveniles in detention in Connecticut's state facilities were studied. Data extracted included self‐reported information on lifetime and daily use of marijuana, mental health indicators, lifetime psychiatric diagnoses and criminal justice indicators. Results Rates of both lifetime (54%) and daily (16%) use of marijuana in this sample of 371 young people were substantially higher than previous studies have reported in general population samples. As a group, daily users of marijuana demonstrated a more negative mental health profile but did not differ from the rest of the sample in their criminal justice indicators. Conclusions/implications for practice Our findings suggest that it is unlikely that cannabis use by young offenders can serve as an independent factor in understanding the frequency and severity of delinquency, although it might be associated with the severity of mental health disorder or dysfunction among them. Copyright © 2014 John Wiley & Sons, Ltd.