Bias in surrogate decision-making can occur when proxy decision-makers overestimate the degree to which their preferences are shared by others, resulting in a projection of their beliefs onto others. The purpose of this study is to assess projection of care partners' preferences onto surrogate assessments of everyday preferences for persons with cognitive impairment (CI) and to address clinical and demographic factors as predictors of projection. The sample included 116 dyads of persons with CI (Clinical Dementia Rating Scale score ≥ 0.5) and their care partners. The Preferences for Everyday Living Inventory (PELI) was used to assess importance of preferences among persons with CI. Care partners completed two separate PELI assessments: one from the perspective of the persons with CI (i.e., acting as a surrogate decision-maker) and one from their own perspective. To assess for projection of care partners' preferences onto surrogate assessments of preferences for persons with CI, two-step regression with multivariable-adjusted general linear models was used. Significant projection was noted within the PELI domains of autonomous choice, personal growth, and keeping a routine (p < 0.005). More significant cognitive impairment was associated with increased projection within the PELI domains of autonomous choice and personal growth (p < 0.05). The results of this study suggest that projection of care partners' own preferences may be a significant source of bias in proxy decision-making regarding everyday preferences for persons with CI, particularly for those with more significant CI.