Purpose: Children’s independent mobility (IM) may facilitate both active transportation (AT) and physical activity (PA), but previous studies examining these associations were conducted in single regions that provided limited geographical variability. Method: We recruited 1699 children (55.0% girls) in 37 schools stratified by level of urbanization and socioeconomic status in 3 regions of Canada: Ottawa, Trois-Rivières, and Vancouver. Participants wore a SC-StepRx pedometer for 7 days and completed a validated questionnaire from which we derived a 6-point IM index, the number of AT trips over a week, and the volume of AT to/from school (in kilometer per week). We investigated relationships among measures of IM, AT, and PA employing linear mixed models or generalized linear mixed models adjusted for site, urbanization, and socioeconomic status. Results: Each unit increase in IM was associated with 9% more AT trips, 19% higher AT volume, and 147 more steps per day, with consistent results across genders. Both measures of AT were associated with marginally higher PA when pooling boys’ and girls’ data. Children in Vancouver engaged in more AT. PA did not vary across site, urbanization, or socioeconomic status. Conclusion: IM was associated with more AT and PA regardless of where children lived, underscoring a need for IM interventions.