Katie Lohmann was born in Scottsdale, Arizona, on January 29, 1980. She is the youngest of three children (sister Christine and brother Michael). Her father Dan is a successful accountant and has owned several businesses. Her mother Sharon is the head of payroll for Citibank. Her parents divorced in 1992.

Katie discovered early on that she loved performing on stage. Her first performance was singing a song from the Walt Disney classic The Little Mermaid (1989), at the age of eight, and she received a standing ovation. In 1989, a casting call took place for the new Disney Mickey Mouse show, "The All New Mickey Mouse Club." Although she had never worked on a TV show, Katie felt that this would be the perfect opportunity and was told she was exactly what they were looking for. However, her mother felt she was too young and the show would interfere with her education. Katie decided to take her mother's advice and wait until she was finished with school before pursuing her career.