The happy post comes just over a week after ET confirmed that McPhee gave birth to her first child with husband David Foster.
As previously reported, ET recently spoke with the performer about her new Netflix series, Country Comfort, when she said she and Foster were feeling great amid her pregnancy.
"I am a little short of breath here and there," she also shared. "Yeah, I mean, some days it's a walk in the park and other days it's like, oh gosh, OK! But, I feel really good. I'm in a good place."
She also revealed how her time on set with her younger co-stars got her even more excited for motherhood.
"Being on set with these kids every day on the show... seeing the different stages of their life is just something to look forward to," she said. "There's always going to be a different stage to look forward to as a new mom."
While this is her first child, 71-year-old Foster has five daughters -- 34-year-old Jordan, 38-year-old Erin, 40-year-old Sara, 47-year-old Amy and 50-year-old Allison -- from previous relationships.