
Kaitlin Willow Olson McElhenney (born August 18, 1975) is an American actress, comedian, and producer. She began her career in The Sunday Company at the Groundlings, an improvisational theatre and school in Los Angeles, California. She had minor roles in several television series before being cast as Deandra "Sweet Dee" Reynolds on the long-running FX comedy series It's Always Sunny in Philadelphia (2005–present).
Olson starred as Mackenzie "Micky" Murphy in the Fox comedy series The Mick (2017–2018) and as Cricket Melfi in the Quibi comedy series Flipped (2020), which earned her a nomination for the Primetime Emmy Award for Outstanding Actress in a Short Form Comedy or Drama Series.
She has also appeared in films including Leap Year (2010), The Heat (2013), Vacation (2015), Finding Dory (2016), and Arizona (2018).
She has been married to actor Rob McElhenney, her co-star on It's Always Sunny in Philadelphia, since 2008.

Finding Dory
2016 · as Destiny (voice)

Incoming
2024 · as Ms. Nielsen

Vacation
2015 · as Arizona Cop

Coyote Ugly
2000 · as Bidding Customer

Leap Year
2010 · as Libby

The Heat
2013 · as Tatiana

Escape from Planet Earth
2013 · as 3D Movie Girl (voice)

Champions
2023 · as Alex

Weather Girl
2009 · as Sherry

Arizona
2018 · as Vicki

A Very Sunny Christmas
2009 · as Deandra "Sweet Dee" Reynolds

It's a Wonderful Binge
2022 · as Mayor Spengler

Held Up
2010 · as Rocky 2

Marine Life Interviews
2016 · as Destiny (voice)

The Nightman Cometh: Live
2009 · as Dee Reynolds

PaleyLive: It’s Always Sunny in Philadelphia 20th Anniversary Celebration!
2025 · as Self

Eyes to Heaven
2000

A Tribute to Ryan Dunn
2011 · as Self