• Nickname is Katie.

• Was contracted with the Elite Modelling Agency and Wilhelmina Modeling Agency.

• She is half Irish and half German.

• Graduated from New Canaan High School class of 1996.

• Played the cello in High School.

• Has played a character with the name of "Isabel" or "Isobel" three times.

• Her parents are divorced.

• Has two older brothers, Holt and Jason; and older sister, Meg.

• Never intended to have a career in televison.

• Beat out Alicia Silverstone for the lead role in My Father the Hero (1994).

• Was to play the role of Kate Libby ('Acid Burn') in the movie Hackers (1995). The role of course went to Angelina Jolie because Katherine opted for Under Seige 2: Dark Territory (1995) instead.

• Auditioned for all 3 female leads on Roswell before being cast as Isabel.

• Found it hard to find a secure job after the end of Roswell, and even planned to leave the industry at one point.

• When Katherine had to do her first underwear scene in Grey's Anatomy she felt very uncomfortable. She jokingly asked the director to strip down as well, and he obliged!

• Is engaged to singer David Kelly (a December 2007 wedding is planned)

• Katherine enjoys relaxing, sitting on one of her big couches with her dogs, reading, knitting, or going to the movies or bar with her fiance.

• Her last name is pronounced "Hye-Gull."

• Rather than see a stylist, Katherine cut and dyed her own hair for the third season of Roswell.

• She has two miniature schnauzers named Anna and Romeo.

• Katherine's mom, Nancy Heigl, is her manager.

• Katherine's brother Jason died when she was young, due to head injuries sustained in a car accident.

• She dated Joseph Lawrence in 1994. They met at Seventeen Magazine's 50th Anniversary party.

• Katherine was once engaged to Jason Behr, her former Roswell co-star. They broke up in 2001.