Son Knox was born in Nashville, and weighed 6 pounds and 12 ounces. He joins sisters Jordan, 1, and Evalyn Day, 5.
"Knox met his big sisters Thursday morning," Bentley's rep told the magazine. "Cassidy is doing great."
The country singer, who wed Cassidy in 2005, first announced in June that they were expecting a boy in a YouTube video.
Bentley's eighth studio album, Riser, is due out later this year.