The Red Cross is a non-profit organization that assists with a variety of scenarios including blood drives and crisis relief during natural disasters and other life threatening events. When you talk about demographics you are looking at the populations that the Red Cross assists on a yearly basis.
When looking at the specific populations that the Red Cross supports it would be 1. Those who need disaster relief regardless of age, race or socioeconomic status, 2. Military families who need help coping with needs specific to being within the military service, 3. International services in third world countries to develop preventative health care, and 4. Preventative medical services through local blood drives as well as teaching first aide and CPR classes.
In short the Red Cross is a strong community resource that individuals can use as part of their social support network, which when working with at risk populations is an important thing to build as at risk populations are often disenfranchised and are not aware of the resources they have at their disposal.