The 'House Bunny' actress and her boyfriend Derek Richard Thomas welcomed daughter Louetta Isley earlier this month.
Rumer captioned the sleeping baby on Instagram: "Louetta Isley Thomas Willis [stars emoji]. "You're magical." "Home-born on Tuesday April 18th."
"You are more than we ever dreamed of (sic)"
The 34-year-old actress had a baby shower last month.
Rumer's mother Demi Moore, stepmother Emma Heming, sisters Tallulah, Scout, Evelyn, and Mabel attended. Peta Murgatroyd, who is pregnant, attended the celebration.
Rumer's pianist boyfriend Derek entertained visitors.
The 'Once Upon a Time in Hollywood' actor told the New York Post's Page Six column: "I feel such gratitude and joy to have been surrounded by so many people that I love."
Rumer's dad Bruce Willis missed the celebration, which was held only weeks after the family announced his frontotemporal dementia (FTD) diagnosis.
"Maybe a week after I became pregnant, it was like, no, no, that's not going to work for me anymore.
"This is what I need to do to reframe this and speak for myself. A fresh equation and problem downloaded instantly.
"And I had a different operating system."