William Cowell Sr. (January 25, 1682 – 1736) was a noted early American silversmith active in Boston.
Cowell was born in Boston, and may have apprenticed with John Allen (1671/72 – 1760), John Edwards (about 1671 – 1746), or Jeremiah Dummer. By 1704 his apprenticeship was complete, and on May 13, 1706, he married Elizabeth Kilby. Samuel Sewall's diary records that in 1707 Cowell's shop was burgled "and a considerable quantity of Plate stolen," although the stolen silver was returned after the thief was apprehended. Seward later records, in 1715, that he hired a horse from Cowell, which is consistent with the profession of "innkeeper" recorded at Cowell's death. He is believed to have retired about 1734 when his son, William Cowell Jr., finished his apprenticeship.
Cowell's work is collected in the Museum of Fine Arts Boston, Metropolitan Museum of Art, Art Institute of Chicago, and Yale University Art Gallery.