With any research endeavor, it is crucial to ask yourself as many questions as possible to ensure you are thinking critically about the subject. For target market research, consider not just the age, but the lifestyle, gender, household size, location, culture, and other factors that would influence that market's consumer tendencies. Alternate your focus between the company/product and the consumer (who would buy X product? would person Y buy it? what prevents them from doing so? what could the company/product do to change this?).
As you research, look for data/information that answers these questions. If you have trouble finding data/information to support your theory, you may be asking the wrong questions, or are trying to shoehorn data to support an answer that you created from the start. Let the research process guide you to the answer rather than begin your research with an answer in mind.
Target market identification is "The process of using income, demographic, and life style characteristics of a market and census information for small areas to identify the most favorable locations." - AMA Dictionary
These resources could help determine target market size for the geographic/market area around Salisbury, MD.