Authors born in 1978
- John Roger Stephens Singer, 1978
- Jose Gonzalez Singer-Songwriter, 1978
- Jose James Vocalist, 1978
- Josh Dallas Actor, 1978
- Josh Hartnett Actor, 1978
- Josh McDermitt Actor, 1978
- Joshua Jackson Actor, 1978
- Josie Maran Model, 1978
- Jukka Nevalainen Drummer, 1978
- Julian Casablancas Singer, 1978
- Justin Brannan Musician, 1978
- Justin Long Actor, 1978
- K. D. Aubert Actress, 1978
- Kara Goucher Runner, 1978
- Karen Denise Aubert Actress, 1978
- Karen O Singer, 1978
- Karina Smirnoff Dancer, 1978
- Karrine Steffans Actor, 1978
- Kat Cole Businesswoman, 1978
- Kate Madison Actor, 1978
- Kate Williams Historian, 1978
- Katharine Towne Actress, 1978
- Katherine Heigl Actress, 1978
- Katherine Parkinson Actress, 1978
- Kathleen Edwards Musician, 1978
- Kathleen Rubins Astronaut, 1978
- Katie Aselton Actress, 1978
- Katie Holmes Actress, 1978
- Katie Price Author, 1978
- Kayvan Novak Actor, 1978
- Kazu Kibuishi Author, 1978
- Keeth Smart Athlete, 1978
- Keinan Abdi Warsame Poet, 1978
- Kel Mitchell Actor, 1978
- Kelly Overton Actress, 1978
- Kenan Thompson Actor, 1978
- Kerri Walsh Jennings Athlete, 1978
- Kevin Federline Rapper, 1978
- Kevin Talley Drummer, 1978
- Kevin Wilson Writer, 1978