The relationships between behaviour, owner-rated personality, and cortisol were examined in companion dogs that visited a local off-leash dog park. In Study 1, salivary cortisol increased significantly from baseline levels following 20min in the dog park (P=0.013), but not in the same dogs following a 20min on-leash walk. In Study 2, cortisol was correlated with dog park visit frequency, such that dogs which visited the park least often had higher cortisol levels (r=−0.34, P=0.013). Hunched posture in dogs was associated with higher cortisol, even after the effect of park visit frequency was removed. Cortisol appeared to be independent of all other measured behaviours and signals indicative of play, stress, agonism, and mounting, as well as dog time budgets. Nor was cortisol related to dog personality scores as measured by the Monash Canine Personality Questionnaire-Revised (MCPQ-R). Scores on the Extraversion, Amicability, and Neuroticism scales predicted some observations in the park: more extraverted dogs showed higher activity (measured as time budget state changes; R2=0.21, P<0.001) and spent more time in conspecific dyads (R2=0.083, P=0.033), more amicable dogs showed more behaviours indicative of play (R2=0.10, P=0.014), and more neurotic dogs showed higher frequencies of hunched posture (R2=0.10, P=0.008). Time budget states correlated with specific behaviours, e.g., focal dog's time spent in dyads correlated highly with total play signals/behaviours in the session (r=0.69, P<0.001). Thus, in a social context such as an off-leash dog park, changes in cortisol may be largely independent of social behaviour/signalling (with the possible exception of postural changes), and personality scores may predict some social behaviours, but not necessarily changes in cortisol. Given that this dog park sample contains dogs which appear to score higher than average for Extraversion, additional relationships between personality, behaviour and cortisol may be detected in broader dog populations and/or other social contexts. As the popularity of off-leash dog parks is increasing in North America, understanding factors related to individual dogs’ experiences in such parks may be important for welfare reasons.