Monitoring the ways in which childhood socioeconomic environment is associated with adult outcomes is fundamental in terms of informing evidence-based policy debates. However, we know little about the cohort differences in the association of childhood income with adult outcomes in Finland, a country of low income-inequality and one of the most desegregated educational systems in the OECD countries. We use longitudinal FOLK register data on complete population cohorts born in 1981-89. We divide these cohorts into tenths by their parental, school and postcode-level aggregated income at the age of 15. We focus on five demographic and socioeconomic adult outcomes at the age of 30. On average across the cohorts, compared to the highest income groups, the lowest tenth of parental, school and postcode income had, respectively, a 1.8, 1.7 and 1.4-fold risk of death, 3, 1.3 and 0.9-fold risk of low education, 2.5, 1.8, and 1.4-fold risk of long-term unemployment. People with a lower childhood parental or school income were more likely to live with a partner and have children than people from higher income backgrounds. The differences by school and postcode income in the education outcome were small, indicating limited school and area segregation in the country. However, we observe increasing absolute and relative differences in the education and employment outcomes by parental and, to a lesser extent, school aggregated income.