The main aim of this study was to explore the correlation between the platelet/high-density lipoprotein cholesterol ratio (PHR) and cognitive function in elderly individuals from the United States. This investigation leveraged data encompassing 2299 participants, all aged 60 years and above, from the National Health and Nutrition Examination Survey conducted from 2011 to 2014. Inclusion criteria were based on the availability of complete datasets for PHR and cognitive function assessments. The analytical approach incorporated multivariate logistic regression to discern the association between PHR and cognitive function. Additionally, the study employed restricted cubic splines (RCS) to explore potential non-linear relationships and subgroup analyses to identify variations in the observed associations across different demographic and clinical subgroups. In the fully adjusted model, an increment of 10 units in PHR was associated with a decline of 0.014 in cognitive scores (β=-0.014, 95% CI: -0.025, -0.002; P < 0.05). Compared to the lowest quartile, participants in the highest quartile exhibited a 38.4% increased prevalence of cognitive impairment per one-unit increase in PHR (OR = 1.384, 95% CI: 1.012, 1.893; P < 0.05). Subgroup analysis revealed consistent results regarding the relationship between PHR and cognitive impairment across all subgroups. A non-linear relationship between PHR and cognitive impairment was observed using RCS, indicating that an increase in PHR above 111.49 significantly elevated the incidence of cognitive impairment (P < 0.05). Our study demonstrates that a higher PHR is associated with a greater risk of cognitive decline in an older U.S. population, and although further validation is needed, this warrants consideration in clinical assessments and interventions.