The 51-year-old country music superstar says he'd like to thank everyone "for their warm wishes and sweet celebration of Baby K's arrival."
Country music's best-selling performer has been in semi-retirement as he raises his daughters in Oklahoma. He'll have another girl around the house now.
August was the second to graduate from high school and Brooks says he's considering a full-time return to recording and performing when his youngest, Allie, graduates from high school next year.
Brooks asked for privacy as "this young family begins the greatest days of their lives."