Background: Child protection services exist to reduce potential harms from child maltreatment. Many jurisdictions produce annual data on child protection system (CPS) involvement, leaving a gap in knowledge of lifetime involvement. Objective: To describe lifetime involvement in CPS, by type of contact. Participants: All 608,547 children born in South Australia (SA), Australia between 1986 and 2017. Methods: A retrospective cohort design using linked administrative data to report cumulative incidence of CPS involvement from birth to age <18 (or June30 2017) by Aboriginal status. CPS involvement was categorised into notifications (3 levels), investigations, substantiations and out-of-home care (OOHC). Cumulative incidence curves were derived for 5 birth cohorts. Results: Across childhood (to age <18 years), substantiated maltreatment was experienced by 3.2–3.6% of non-Aboriginal and 19–25% of Aboriginal children, 7 times reported annual substantiation rates. For most CPS categories CPS involvement increased until 2010, and was occurring earlier in life. By age 3, 0.5% of non-Aboriginal and 4.5% of Aboriginal children born 1986–1991 were the subject of a substantiation compared with 1.9% and 15% of non-Aboriginal and Aboriginal children, respectively, born 2010–2017. Incidence rates beyond age 3 were similar. OOHC contact was similar across cohorts, with ˜1.5% of non-Aboriginal and 12.7% of Aboriginal children ever-placed in care. Conclusions: Data linkage is an essential tool for understanding life course involvement with the CPS and describing trends not observable from annual snapshots. Such information is critical for burden of disease estimates, informing policy and monitoring CPS performance.