Background: Depression among adolescents has been recognized as a public health problem all over the world. In Nigeria, as in most developing countries, there is a need for more research on the epidemiology of adolescent depression as this will guide prevention, diagnosis and treatment. Objectives: The study sought to determine the one month prevalence and predictors of depression among a sample of in-school adolescents in a rural region in South West Nigeria. Materials and Methods: This was a cross sectional descriptive survey among 540 secondary school students randomly selected from the six secondary schools in the study area using a Socio demographic Questionnaire and the Patient Health Questionnaire modified for Adolescents. Subsequently, a proportion of them were interviewed with the Kiddies Schedule for Affective Disorders and Schizophrenia. Results: Data were analyzed using the SPSS version 17. Respondents were aged 10 -19 years (mean age was 14.07 ± 1.84). The one month prevalence of depression among the study population was 16.3% (using weighting method). Logistic regression analysis showed that death of a mother (OR = 11.786, 95% CI, 1.990 -23.184), being from a polygamous family (OR = 5.781, 95% CI, The one month prevalence of adolescent depression within the study population is slightly higher than what has been reported in other parts of the world. Therefore, there is a need for government to design and implement policies which can help to prevent, detect early, and treat depression among youths especially in rural areas.