Objectives: To examine the association of social network size and loneliness with cognitive performance and -decline in depressed older adults. Method: A sample of 378 older adults [70.7 (7.4) years] with a Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition diagnosis of current depressive disorder were recruited from primary care and specialized mental health care. Cognitive performance was assessed at baseline and 2 years follow-up with the Stroop colored-word test, a modified version of the Auditory Verbal Learning Task and the Digit Span subtest from the Wechsler Adult Intelligence Scale, encompassing four cognitive domains; processing speed, interference control, memory, and working memory. Social network size was assessed with the Close Person Inventory and loneliness with the de Jong Gierveld Loneliness Scale at baseline. Results: After adjusting for baseline working memory performance, loneliness was associated with impaired working memory after 2 years [B = −0.08 (−0.17 to 0.00)]. This association was no longer significant after adjusting for age, sex, education level, physical activity, alcohol use and depressive symptom severity [B = −0.07 (−0.16 to 0.03)]. A backward elimination procedure revealed education level to be the only covariable to explain this association. Loneliness was not associated with impairments or decline in other cognitive domains. Social network size was not associated with cognitive impairments or decline. Conclusion: Social network size and loneliness do not predict cognitive decline in depressed older adults.