Background and Objectives: Physical activity (PA) environments at micro- (eg, home) and macro-levels (eg, built) may be associated with rural children’s PA, an underrepresented population in research. A secondary data analysis of New Ulm at HOME, a family-based childhood obesity prevention RCT, examined which environmental supports explain variation in moderate-to-vigorous PA (MVPA), vigorous PA (VPA), and total PA. Methods: Gold standard measurement tools (geospatial analysis; accelerometry) and surveys were used to assess children’s (N = 105, age 7-10) PA environments and behaviors. Environmental supports were evaluated in a block-wise manner. Each variable was placed into 1 block (ie, sociodemographic characteristics, physical supports, or social supports). Blocks were added in a sequential manner to multiple linear regression models, controlling for sociodemographic variables, and analyzed for their groupwise ability to explain variation in MVPA, VPA, and total PA. Results: At micro- and macro-levels, differences in MVPA were explained by physical supports (ΔR2 = 0.06, P = .03; ΔR2 = 0.13, P = .04). Explained variance in VPA was improved by neither physical nor social supports at either level. Physical supports explained differences in total PA at the micro- (ΔR2 = 0.09, P = .01) and macro-levels (ΔR2 = 0.17, P = .01). Conclusions: Further research is warranted to explore if expanding access to PA equipment and infrastructure supports mitigates inactivity in rural youth.