Frank Miles Day (April 5, 1861 – June 15, 1918) was a Philadelphia-based architect who specialized in residences and academic buildings.
In 1883, Day graduated from the Towne School of the University of Pennsylvania, and traveled to Europe.
In England, he apprenticed under two architects, and won the 1885 prize from the Architectural Association of London.
After his apprenticing in England, Day returned to Philadelphia, where he worked with George T. Pearson and Addison Hutton prior to opening his own office in 1887.
Day died June 15, 1918, and is interred at West Laurel Hill Cemetery in Bala Cynwyd, Pennsylvania.