Martha Campbell Plimpton (born November 16, 1970) is an American actress, singer, and former model. Her feature film debut was in The River Rat (1984) before rising to prominence in the Richard Donner film The Goonies (1985). She has also appeared in The Mosquito Coast (1986), Running on Empty (1988), Parenthood (1989), Samantha (1992), Raising Hope (2010) and Small Town Murder Songs (2011).

She is recognized on Broadway for her roles in The Coast of Utopia (2006–2007), Top Girls (2007–2008), Pal Joey (2008–2009) and Shining City (2006–2007). She has performed in theatre productions of The Playboy of the Western World, A Midsummer Night's Dream, The Glass Menagerie, The Sisters Rosensweig, and Uncle Vanya. She returned to Broadway in the fall of 2014 in a revival of A Delicate Balance co-starring Glenn Close and John Lithgow.

Plimpton most recently starred in The Real O'Neals, an ABC sitcom that aired from March 2016 to March 2017. In 2009 Plimpton portrayed a helpless mom being robbed by two criminals in the music video "Bully" by Three Days Grace.

Plimpton played Virginia Chance on the Fox sitcom Raising Hope, which earned her a Primetime Emmy Award nomination for Outstanding Lead Actress in a Comedy Series. She has also received three Tony Award nominations as well as a Primetime Emmy Award nomination for Outstanding Guest Actress in a Drama Series in 2002, and again in 2012 as attorney Patti Nyholm in the CBS legal drama The Good Wife.