The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Bricklaying (1 member)
- Brindabellas (1 member)
- Broodiness (1 member)
- Bugs (4 members)
- Building (2 members)
- Bus stops (1 member)
- By the Ionian Sea (1 member)
- C.F. Barker Archives (1 member)
- CLI (1 member)
- CSV (2 members)
- Cafes (0 members)
- Cafés (8 members)
- Calendar (1 member)
- Calendars (1 member)
- Camping (1 member)
- Canberra (21 members)
- Captains Lane (1 member)
- Cargo (0 members)
- Carnival (1 member)
- Carrington Street (2 members)
- Cars (3 members)
- Cartography (1 member)
- Casio (1 member)
- Catalogues (1 member)
- Cataloguing (2 members)
- Categories (33 members)
- Categorisation (1 member)
- Cats (0 members)
- Causes (1 member)
- Centenary Building (1 member)
- Changes (1 member)
- Chicago Manual of Style (1 member)
- Chickens (3 members)
- Childhood (1 member)
- Chronology (5 members)
- City of Fremantle (1 member)
- Clare Davies (1 member)
- Climate change (1 member)
- Clontarf Road (2 members)
- Closeness (1 member)
- Clothing (1 member)
- Cloud storage (2 members)
- Cmd (2 members)
- Co-op (1 member)
- Co-operative (1 member)
- Cockburn (1 member)
- Code (5 members)
- Code projects (1 member)
- Code snippets (1 member)
- Coding (3 members)