He graduated from the medical department of the University of Maryland at Baltimore in 1816 , and practiced his profession in Harford , Baltimore , and Cecil counties .
Born in Bel Air , Maryland , Preston attended the common schools .
Preston graduated from the medical department of the University of Maryland at Baltimore in 1816 , and practiced Preston 's profession in Harford , Baltimore , and Cecil counties .
Born in Bel Air , Maryland , Preston attended the common schools .