Los Angeles County Chief Coroner Investigator Craig Harvey says the examination will be held Tuesday for the 30-year-old Johnson.
He says he cannot provide other details and didn’t immediately confirm police statements there were no signs of foul play.
Police officers responded to her Los Angeles home around 11:51 a.m. where paramedics had already pronounced Johnson dead, officer Sara Faden said.
Faden said she did not know how long Johnson may have been dead, but did say her death may have been from natural causes since a preliminary investigation turned up no signs of foul play.
Johnson had diabetes, but it was unclear whether that was a factor in her death.
Harvey says he cannot provide other details and didn’t immediately confirm police statements that there were no signs of foul play.
Faden added that a final cause of death will be determined by coroner’s officials, who will seek toxicology tests. Results of those tests could take six weeks to obtain.
"The Johnson family is mourning its tragic loss, and asks for privacy during this very difficult time," Johnson family spokesman Jesse Derris said last night.
Johnson had a 3-year-old daughter, Ava Monroe, whom she adopted from Kazakhstan in 2007. Ava has been in the custody of Johnson's mother, Sale Johnson.
Back in October, Johnson made headlines after having a nasty fight with her former girlfriend, Courtenay Semel, daughter of former Yahoo! chief Terry Semel, in which her hair caught fire. Then in November, she was arrested for allegedly burglarizing a model's home.
Last month, TV personality Tila Tequila announced that the two were engaged and that she planned to adopt Johnson's daughter.
Tequila posted a message on her Twitter page Monday acknowledging Johnson's death, thanking well-wishers for their words of comfort.
"Everyone please pray 4 my Wifey Casey Johnson," she wrote. "She has passed away. Thank u for all ur love and support but I will be off-line to be w family."
Tequila later tweeted, "R.I.P my Angel. u will forever be in my heart! I love u so so much and we will Marry when I see U in Heaven."
She then spoke with TMZ.com, telling the Web site that she and Johnson had been fighting last week and that she had been unable to contact her since Dec. 29.
Johnson, a high school classmate of fellow socialite Paris Hilton, told Vanity Fair in a 2006 interview that her decision to turn down Hilton’s invitation to be her co-star on “The Simple Life” was “the stupidest mistake of my life.” Hilton eventually chose Nicole Richie.
“I kick myself in the butt everyday,” she told the magazine.