The
Chéran forms part of the commune's eastern border, crosses the village, flows north-northwestward through the northern part of the commune, then flows into the
Fier, which forms part of its northern border. Rumilly forms an
urban unit with the adjacent, smaller commune
Sales.
Climate Rumilly has an
oceanic climate (
Köppen Cfb) in spite of its relatively far inland position. Influenced by its elevation, summers are rather moderate on average, although they can be highly variable with extreme heat spikes. Winters see occasional freezing temperatures, but most often stays in the single-digits during daytime with frequent cold rain.
Air frosts are normal during the night and snowfall is not uncommon. ==Population==