The 57-year-old actor, best known for his role as Stanford Blatch on the show, passed away after losing his battle with cancer.
Famous friends took to social media on Tuesday evening to pay their respects and remember Willie, and now Kristin has posted a statement on Instagram, recalling her career highlights with Garson.
"I first met Willie in 1995 on the spooky nighttime set of The X-Files," she wrote alongside a photo of the actor with his son. "He immediately made me laugh. Little did I know that we would have the joy of sharing Sex and the City + (upcoming series) And Just Like That… together."
"Willie is beloved by our entire community. He was smarter and funnier than you ever would have imagined. We are bereft without him."
She added, "But I really want to pay tribute to his fearless commitment to single fatherhood. We spoke about being single parents through adoption often. And nothing gave him more joy and pride than his son Nathen... I am thankful for all of the time we had and grateful that so much of your bright light is on film forever... We love you forever."
Kristin's "Sex and the City" co-stars David Eigenberg and Evan Handler, who will also appear in the new follow up series, have also shared tributes to Garson.
David called the late actor "the kindest most beautiful beautiful man," adding, "Sleep well my friend. You will always be remembered."
And Evan wrote, "This is a tragedy for the entire #SATC #AJLT family, for Willie's family, and for the world. Willie was a prince, the Mayor of every group he ever existed within, and - most importantly - a parent. My heart grieves for his son. A consumate (sic) funny man. Bless you."