Mia Dillon (born July 9, 1955) is an American actress.

Born in Colorado, Dillon made her Broadway debut in Da in 1978. She was nominated for the 1980 Drama Desk Award for Outstanding Featured Actress in a Play (Once a Catholic) and the 1982 Tony Award for Best Featured Actress in a Play (Crimes of the Heart). Additional theater credits include Agnes of God, The Corn is Green, Hay Fever, Come Back, Little Sheba, The Three Sisters, and Our Town. On television, Dillon co-starred in Mary and Rhoda and has appeared in all three current shows in the Law & Order franchise. Her screen credits include The Money Pit, A Shock to the System, Gods and Generals, and Duane Hopwood.

Dillon has been married to actor Keir Dullea since 1999. They split their time between an apartment in Manhattan and a home in Connecticut.

Presently on the staff of StoneStreet Studios (N.Y.), Acting Workshop.

Nominated for Broadway's 1982 Tony Award as Best Actress (Featured Role - Play) for "Crimes of the Heart."