Antidepressant prescription for youths has recently been on the increase. There is a growing concern over the increasing off-label usage of antidepressants. Current data on off-label antidepressant usage vary across countries and healthcare systems. Therefore, we examined the extent and pattern of antidepressant prescription for Korean children and adolescents using population-based data. Our data was retrieved from the Korean National Health Insurance Service National Sample Cohort of the year 2013. Among 0.2 million children and adolescents aged 6–18 years from the cohort, subjects who had received any antidepressant medication in the year 2013 were investigated for the prescribed medication, concomitant psychotropic medication, and the associated diagnosis. A total of 2,190 children and adolescents (boys, 55.4%) received antidepressant medication. The most common diagnosis was depressive disorders (n = 469, 21.4%), followed by attention-deficit/hyperactivity disorder (n = 442, 20.2%). Among the prescriptions (n = 3,370), escitalopram (n = 650, 24.1%) and fluoxetine (n = 553, 20.5%) were the two most frequently prescribed drugs. A majority of prescriptions (n = 2,039, 60.5%) included concomitant psychotropic agents, consisting of antipsychotics (n = 901, 26.7%), sedatives (n = 263, 26.3%), medication for attention-deficit/hyperactivity disorder (n = 822, 24.4%), and some others. Our study shows the prescription pattern of antidepressants for children and adolescents in Korea, of which a large proportion is off-label. The results call for close monitoring by clinicians treating this population.