Background: The System of Observing Play and Leisure Activity in Youth (SOPLAY) has assisted in providing valid and reliable data of youth physical activity and characteristics specific to environmental contexts. The review aimed to examine empirical research that employed the SOPLAY instrument to measure physical activity in leisure-based activity environments in North American countries. Methods: The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. A systematic search was conducted with an exhaustive process using 10 electronic databases to locate peer-reviewed studies implementing SOPLAY that were published between 2000 and 2021. Results: A total of 60 studies were included in the review. Most studies (n = 35) reported physical activity findings related to contextual characteristics measured using SOPLAY. Interestingly, a few of the studies (n = 8) found the provision of equipment and supervision, particularly adult supervision, significantly increased child physical activity observed. Conclusions: This review provides information relative to the group-level physical activity observed across multiple contexts (i.e., playgrounds, parks, recreation centers) using a validated direct observation instrument.