Objective: To use routinely-collected maternity healthcare data to 1) describe the prevalence of key preconception indicators (e.g., smoking, folic acid supplement use) and 2) explore differences in prevalence by area-based level of deprivation. Design: Retrospective population-based study. Setting: Northern Ireland (NI). Population: 255,177 pregnancies recorded in the Northern Ireland MATernity System (NIMATS). Methods: Anonymised NIMATS data recorded during antenatal booking appointments (2011-2021) were accessed through the Honest Broker Service and analysed using R. Prevalences were calculated for each indicator, overall and based on deprivation quintile. Logistic regression models explored the relationships between each preconception indicator and area-level deprivation quintiles. Patient and Public Involvement and Engagement representatives helped prioritise indicators to include in the study, in conjunction with consulting the current evidence base, availability in NIMATS, and indicator modifiability. Main Outcome Measures: Preconception indicators, including behavioural factors (e.g., planned pregnancy), pre-existing health conditions (e.g., severe mental health), and area-based deprivation. Results: A high proportion of women had sub-optimal preconception indicators (e.g., 21.3% living with obesity). Women living in the most deprived quintile generally had a higher prevalence of risk factors than women in the least deprived quintile (e.g., smoking prevalence was 25.7% in the most deprived quintile and 5.6% in the least deprived quintile). Conclusions: Population-based maternity data in NI highlight many areas of women’s preconception health that require improvement and support, especially for women living in the areas of greatest deprivation. Findings are an essential reference point to inform interventions, policy, and ongoing monitoring of preconception health in NI.