Söderby is a village in Eskilstuna Municipality, in Södermanland County, Sweden. Söderby lies at 28 m above sea level. The nearest city is Eskilstuna, 15.4 km to the west. Among the landmarks around are Strängnäs Cathedral (14.3 km), Gripsholm Castle (28 km) and Jäder Church (7.1 km).