William Parker Halliday (July 21, 1827 – September 22, 1899) was an American steamboat captain, banker, printer, hotel owner, vast landowner and businessman. Halliday began his professional career working on steamboats on the Mississippi and Ohio rivers and eventually became a captain of a steamboat based out of Louisville, Kentucky. A pioneer in the river and railroad transportation businesses, Halliday was responsible for the expansion of Cairo, Illinois, following the American Civil War.