River otter populations have expanded across much of their historical range, including in Illinois where they were reintroduced from 1994 to 1997. These expanding populations are recolonizing a wide range of landscapes with different levels of human modification, which could influence how river otters use space in relation to habitat characteristics and each other. Our objectives were to quantify 1) home ranges and core areas, 2) sociality, and 3) habitat selection across all available habitats and within home ranges (second- and third-order selection, respectively) of 22 radiomarked river otters (Lontra canadensis) in southern Illinois during 2014–2016. Our study area contained a diverse mix of forest, agriculture, aquatic and wetland habitats, and a range of urban development intensity. We examined sociality using the frequency at which individuals were located < 25 m from a conspecific and compared home-range overlap among individuals based on sex. Habitat selection at the second and third order was analyzed using an eigen-analysis of selection ratios based on landcover categories. Similar to other studies, male river otters had > 2-fold larger home ranges and core areas than females in southern Illinois. Several lines of evidence indicated males were more social than females. Males were located close to a conspecific more frequently than were females, and overlap of home ranges and core areas among males was greater than it was among females or between sexes. As observed in other landscapes, river otters strongly selected herbaceous and wooded wetlands at both second- and third-order scales. River otters selected terrestrial cover types with vegetative cover potentially due to shelter or prey availability. Forests were selected over crop fields at the third-order scale, which was consistent with studies using sign surveys. River otters in our study had home ranges containing 0–40% developed land cover, but we found no evidence that otters living in more developed areas used their home ranges more selectively. River otters in this landscape were plastic in regard to social behavior and habitat selection, highlighting their generalist nature and providing insight into their ability to successfully recolonize areas of the Midwest with sufficient vegetative cover and aquatic habitat, among other factors.