The 19-year-old daughter of former Alaska Gov. Sarah Palin earlier this month called off her re-engagement to the 20-year-old Johnston.
On Friday, Palin family attorney Thomas Van Flein confirmed a report that the couple have agreed on custody. He says Palin gets primary physical custody of the little boy and they share legal custody, subject to her resolution if they can't agree.
The lawyer adds that Johnston gets visitation on Wednesdays and Saturdays.
Van Flein says Johnston will pay child support based on anticipated earnings of $72,000 per year.
A report of the agreement appeared on TMZ.com.
The couple broke off their first engagement soon after Tripp was born in December 2008.