Objectives: Secondhand smoking may contribute to cognitive decline, but evidence on this subject is limited in the working economically active older adults. This study aimed to investigate the association between cognitive decline and exposure to secondhand smoke at work in economically active adults aged 65 years or above. Study design: Cross-sectional study using nationwide data. Methods: Data were from the 2022 Korea Community Health Survey. Chi-squared test was used to perform descriptive statistics. The association between cognitive decline and exposure to secondhand smoke at work was analysed using multivariable logistic regression analysis. Subgroup analysis was performed based on to exposure status to secondhand smoke at home and diabetes mellitus. Results: Of a total of 28,197 adults, 8767 (28.5%) individuals reported cognitive decline. Compared to individuals without exposure to passive smoking at work, those with such exposure were more likely to report cognitive decline (odds ratio: 1.30, 95% confidence interval: 1.14–1.47). This association was particularly strong in individuals with exposure to passive smoking at both work and home and in those diagnosed with diabetes mellitus. Conclusions: Exposure to secondhand smoking at work is associated with a higher likelihood of cognitive decline in older-aged economically active individuals. The findings infer the importance of monitoring passive smoking and implementing public health measures to reduce workplace secondhand smoke exposure.