Opossums are active year-round and inhabit moist woodlands and brushy habitats at low elevations. They are common to abundant throughout California west of the Sierra Mountains. The preferred habitats include riparian, moist woodlands, brushy habitats, wetlands, agricultural areas, and residential areas that provide abundant food and cover. Water is required for species success so higher concentrations may be found near water sources, especially during dry years. Dense conifer forests and grasslands do not seem to support large numbers.
Activity occurs throughout the night from dusk to dawn, peaking at midnight.
During periods of extreme cold they are far less active and may be active during the day. They may also remain inactive for several days in their burrows during the winter. Fat is accumulated in the fall and used as energy during these cold periods when food may be limited. Rough nests of leaves and other material is constructed in hollow logs, snags, rocks, piles of brush, or in the burrows of other animals. They have also been documented using man-made structures such as buildings and culverts.