Baby Dylan was born around 4 p.m., weighing in at 7 lbs., 11 oz.
DeMarcus, 41, was in Detroit for a Rascal Flatts performance on Friday, but made it to Nashville just in time to welcome his second child into the world.
The singer returned to Detroit just hours later for the show in his hospital scrubs.
Dylan joins big sister Madeline Leigh, age 19 months.
Jay and his wife married in 2004. Allison is a former Miss Tennessee.
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