The couple already have a daughter, Tallulah Fyfe, 4. They met in 1994 when she cut his hair at a salon, and were married five years later at his family's Maine farmhouse, People reported.
Dempsey played Reese Witherspoon's fiance in "Sweet Home Alabama" in 2002. He had been a star as a teenager.
About balancing an acting career with his personal life, Dempsey said, "I really love it now. But I also have a life outside it with Jill and Tallulah. I am really thankful that it is all going well."