This study tested the feasibility, reliability, and validity of the MotionWatch 8 among assisted living residents with and without cognitive impairment. Data from the Dissemination and Implementation of Function Focused Care in Assisted Living Using the Evidence Integration Triangle study were used. The sample included 781 individuals from 85 facilities with a mean age of 89.48 (SD = 7.43) years. The majority were female (71%), White (97%), and overall (44%) had cognitive impairment. A total of 70% were willing to wear the MotionWatch 8. Reliability was supported as there was no difference in time spent in activity across three consecutive wear days. Validity was based on hypothesis testing, and function was associated with counts of activity at baseline (p = .001) and 4 months (p = .001). Those with cognitive impairment engaged in less physical activity (p = .04). The MotionWatch 8 is a useful option for measuring physical activity in older adults with and without cognitive impairment.