Community parks have achieved recognition as a public health intervention to promote physical activity. This study evaluated changes in population-level physical activity when an undeveloped green space adjacent to transitional housing for refugees was transformed into a recreational park. A prospective, nonrandomized study design used the System of Observing Play and Recreation in Communities (SOPARC) to document the number and activity levels of park users over time, and to compare trends pre- and post-construction. T-tests or tests of medians (when appropriate) were used to compare pre- and post-construction changes in use of non-park and park zones for physical activity and changes in park use by age and gender. Pre- and post-comparisons of people observed using non-park zones (i.e., adjacent streets, alleys and parking lots) and park zones indicated a 38% decrease in energy expended in non-park zones and a 3-fold increase in energy expended within the park (P = 0.002). The majority of park users pre- and post-construction were children, however the proportion of adolescent males observed in vigorous activity increased from 11% to 38% (P = 0.007). Adolescent females and elderly continued to be under-represented in the park. Our findings support an association between creation of accessible outdoor spaces for recreation and improvements in physical activity. Community involvement in park design assured that features included in the park space matched the needs and desires of the communities served. Some demographic groups were still under-represented within the park, suggesting a need to develop targeted outreach strategies and programming.