Background/Objectives: Guided by the Social Ecological Model, this study examined the relationships between ecological environmental factors, executive function, physical activity, and sedentary behavior among youth. Methods: A cross-sectional study was conducted among 283 youth (M_age = 15 years; Male = 33.6%) in the North Texas region. Parent-report surveys were used to assess ecological environmental factors, executive function, physical activity, and sedentary behavior. Sociodemographic characteristics, including household income, ethnicity, age, and sex were also collected. Results: Neighborhood safety/crime was significantly associated with all components of executive function (p < 0.01). Community walkability was significantly associated with overall executive function and planning (β = 0.16 and 0.18, p < 0.05) and with screen-based sedentary behavior (r = −0.23, p < 0.01). Neighborhood safety/crime and the home media environment significantly predicted physical activity (β = −0.34; β = −0.29, p < 0.01; R² = 20.4%), whereas the socioeconomic environment emerged as a significant predictor of daily sedentary behavior (β = 0.16; p < 0.05; R² = 18.1%). The mediation model showed acceptable fit, chi-square (df = 25) = 420.32, p = 0.017, CFI = 0.956, and RMSEA = 0.050, 90% CI [0.021, 0.075]. The direct path from environmental factors to executive function was statistically significant (p < 0.01); however, the indirect effect of environmental factors on executive function through physical activity was not supported. Conclusions: These findings suggest that neighborhood safety and walkability are associated with executive function in school-aged youth, independent of physical activity levels. Because the data are cross-sectional, these implications should be tested in longitudinal and intervention studies before informing clinical guidelines.