Winter's Modern Family costar Sofia Vergara took to Instagram to share a picture of the new adult blowing out the candles on a cake.
"Happy bday @arielwinter," she captioned the shot with several party emojis.
Nolan Gould, who plays Winter's brother on the hit show, shared his own picture of her on the big day on Instagram.
"We started Modern Family when we were 11 years old. Today, Ariel is now an adult. It's been amazing spending these last 7 years together. Happy birthday!!" wrote Nolan, 17.
The rest of Winter's costars also made it a point to send the birthday girl a sweet message.
"Happy 18th birthday @arielwinter! You are such a kind, talented, and beautiful woman and it's been fun getting to grow up with you for the past 10 years," wrote Rico Rodriguez, 17. "Cheers to many more birthdays together!"
"Happy birthday to the sweet, adorable and wildly talented @arielwinter1. My promise to have Ed O'Neill crush anyone who hurts you remains," quipped Eric Stonestreet on Twitter.
Happy birthday to the sweet, adorable and wildly talented @arielwinter1. My promise to have Ed O'Neill crush anyone who hurts you remains.— Eric Stonestreet (@ericstonestreet) January 28, 2016
Echoed Jesse Tyler Ferguson on Instagram, "Happy Birthday to the beautiful and talented @arielwinter. I can't believe I've watched her grow up before my very eyes. She is one of the smartest, strongest & most inspiring women I know...and she's only 18! [love] you Ariel!"
Sarah Hyland, Winter's on-screen sister, also shared her own Instagram of the two.
"Happy 18th birthday @arielwinter!!!!! It blows my mind that you're now the age I was when we first met," she captioned a shot of the two smiling at each other on the beach in wetsuits. "Love you little sister."
Later in the evening, it appears that Winter celebrated with dinner at Nobu with her boyfriend Laurent Claude Gaudette, who shared a short video of the two kissing on Instagram.
"Had the pleasure of spending the day with this beautiful and perfect birthday girl," her wrote. "Happy Birthday love."
Winter shared her own video, writing: "Pre Nobu Nobu Nobu @laurent_claude_gaudette."