Using neighborhood open spaces (NOS) may be an easy way for older adults to maintain healthy aging through physical activity and social interaction. Little is known about older adults' use of NOS, their preferences, and barriers to using them. This paper presents older adults' use of NOS in a deprived neighborhood before and after an intervention and factors promoting or inhibiting their use using convergent mixed methods design. Participatory research was employed involving older adults in the intervention. The System for Observing Play and Recreation in Communities was used to observe older adults' use of 13 NOS in spring 2017 (baseline) and spring 2018 (follow-up). Ten interviews were conducted in 2018 to identify barriers and facilitators for using NOS. Two NOS had a pavilion built and, in one NOS, benches were renovated, including building raised flower beds and small tables. At baseline, 209 older adults were observed, whereas 329 were observed at follow-up. More (44%) older adults were observed at follow-up in the NOS with the renovated benches. No use of the two pavilions was observed. The interviews identified six factors important for older adults' use of NOS: weather, support for social caretakers, support for resourceful volunteers, organized activities, social interaction, and sense of ownership. Organizational resources, such as social caretakers and volunteers, are important to promote older adults' use of NOS. Social interaction is a key factor for older adults' use of NOS and should be prioritized by health promoters.