Purpose The purpose of this study was to develop and psychometrically test the Diabetes Caregiver Activity and Support Scale (D-CASS), a measure of how difficult or easy caregiver activity and supportive behaviors are for family caregivers of persons with type 2 diabetes (T2DM). Methods Internal consistency reliability, test-retest reliability, criterion-related validity, and construct validity were examined in 101 family caregivers of persons with T2DM. Participants were recruited using study brochures distributed at a large hospital in the Midwest and at statewide American Indian Pow Wows. Additionally, study brochures were available via a link on Facebook. Data collection occurred by telephone, face-to-face, or through Facebook using measures with evidence of reliability and validity. Family caregivers were predominately female (82.2%), spouses (50.2%), and American Indian (17%), African American (24%), or white (55%). Data were analyzed using descriptive statistics and psychometric analyses. Results The psychometric analyses resulted in an 11-item D-CASS with evidence of internal consistency reliability (alpha = .82) and test-retest reliability. Evidence of construct validity was obtained using 3 hierarchical multiple regressions guided by a conceptual model. Factor analysis supported the unidimensionality of the D-CASS. Conclusion The 11-item D-CASS is a brief and easy to administer instrument that has evidence of reliability and validity in family caregivers of persons with T2DM.