The 23-year-old 19 Kids & Counting star and Dillard announced the news in an interview for People magazine's September 1 issue.
"We're having a baby!" Duggar revealed. "We are so excited."
"It was surreal," Dillard added. "We were shocked. Both of us are so excited!"
Duggar and Dillard have been together since November 2013, and married on June 21 in front of their family and friends. The pair are both devout Christians, and saved their first kiss for their wedding day.
"About 30 days after Jill and Derick got married they gathered everyone in the living room and shared the news," Duggar's father Jim Bob detailed. "Everyone was clapping and cheering, and we were in shock, too."
Duggar and her family currently star on TLC series 19 Kids & Counting. Jill is fundamentalist Baptists Jim Bob and Michelle Duggar's second-eldest daughter, and younger sister Jessa got engaged to Ben Seewald last week. The reality show will return for a ninth season September 2.