James Sidney Mercer (1881 - June, 1945) was an American sports writer who covered mostly boxing and baseball in St. Louis, Missouri and in New York City.
Mercer was born in Champaign County, Illinois, and began his career as a printer's apprentice with the St. Louis Republic.
He later wrote for the St. Louis Post-Dispatch, before the St. Louis Browns hired him as their road secretary in 1906. The following year, Mercer was hired at the New York Evening Globe. He later wrote for the New York Evening Journal and Hearst's American (later known as the New York Journal American). He died in 1945.
He was awarded the J. G. Taylor Spink Award by the National Baseball Hall of Fame and Museum in 1969.