- 4 Classical Institute
- 7 Classical Revival (European revival style)
- 3 Classrooms
- 1 Clavichords
- 3 Claxton, Remsen & Haffelfinger
- 2 Clay, Cosack & Co.
- 3 Clay, Henry, 1777-1852
- 3 Cleaners
- 7 Cleaning
- 1 Clearfield Chemical Works-William Adamson
- 3 Clearfield County, Pennsylvania
- 8 Clearfield Street
- 1 Clearfield Textile Machine Co.
- 1 Clearview Street
- 1 Cleavers (culinary tools)
- 1 Clein, Francis, 1582-1658, active in England
- 9 Clemens, Samuel Langhorne, 1835-1910
- 3 Clement I, Pope
- 2 Clement, E. School
- 2 Clement, William James, 1802-1870
- 3 Clementine Street
- 1 Cleopas (Biblical figure)
- 2 Cleopatra (Sculpture)
- 30 Clergy
- 2 Clerks
- 4 Cleveland Street
- 1 Cleveland Worsted Mills
- 17 Cleveland, Ohio
- 7 Cliffs
- 4 Clifton Heights, Pennsylvania
- 1 Climate change
- 2 Climbing
- 2 Clinics
- 1 Clinics (institutions, medical)
- 3 Clinton Manufacturing Co.
- 1 Clinton Shipbuilding and Repairing Co.
- 1 Clinton Street
- 2 Clipper ships
- 1 Clippers (cutting tools)
- 20 Clippings
