Education is a well-established determinant of cognitive functioning in later life. Prior research has, however, largely focused on the vertical dimension of education, i.e., the quantity of education received, and neglected horizontal stratification within levels of education. A key dimension of horizontal stratification in higher education is field of study. Many studies have found large differences in the economic returns to educational degrees by field of study. It is possible that the benefits that educational degrees have for later-life cognition may likewise vary by field of study. Using nationally representative data from the High School & Beyond (HS&B:80) cohort study we examine whether the associations between educational degrees and cognitive functioning at age ~60 vary by field of study. A key methodological challenge is to account for selection into fields of study. HS&B:80 has followed its sample members since they were in high school, which allows us to account for a wide range of prospectively-collected pre-college covariates. Our analyses show that the strength of the association between educational degrees and cognitive functioning in late midlife significantly differs by field of study. This holds when adjusting for a comprehensive set of covariates including indicators of the individuals’ socioeconomic background, high school test scores, high school GPA, and aspirations in high school. The findings highlight that cognitive aging researchers should not only look at the vertical dimension of education but also consider stratification within levels of education. Moreover, the findings may have implications for disparities in later-life cognitive functioning given differences in fields of study by gender, race, and socioeconomic background.