The "Shake It Off" hitmaker kicked off her own special day by taking to Instagram and sharing a photo of herself as a kid for social media's Flashback Friday trend.
"Who's gonna tell her she's thirtay (sic) now," Swift captioned the childhood image, in which she was featured wearing a colourful tie-dye dress with blue shorts.
Famous friends then began flooding Instagram with birthday wishes in honour of Swift's age milestone, with model Hadid uploading snaps of the pair hanging out, and writing, "My T ! An old soul celebrating 30 years here ... and what a phenomenon you are. It's rare someone can be inimitable yet still make hearts feel at home with innate generosity. I love you and can't wait to celebrate you sister !!!! HAPPY BDAY @taylorswift".
Commenting on the post, Reese Witherspoon added, "Happy BIRTHDAY TS!!".
"Girls" star Dunham also shared a picture of Swift cuddling up to a pet cat, and heaped praise on the birthday girl's many talents.
"This woman is turning 30 today and what can I say. She can cook a lasagna or a lemon drizzle cake. She can cut your cat's nails gently and even knows the term 'dew claw'," detailed Dunham.
"She can style an outfit, paint a birthday gift by hand, plan a day that feels like an hour. She can fix a broken heart (not just with her music but with her love and wisdom.) She can dance (both hot and goofy.) She can unite friends and send the best links of the week and also, oh I forgot, slay the forces of oppression for female artists and become an irreplaceable icon," the actress continued, referencing Swift's industry battle with Scooter Braun over her masters.
Dunham went on to applaud the musician's ability to find the "magic" in everything, and concluded: "Tay, I love you- more than we love caffeine, the real estate section or even- yes even- cats. Thank you for letting me watch you grow into this woman of wild grace...".
Meanwhile, veteran singer/songwriter King dug out an old photo of the two artists and captioned it, "Happiest birthday @taylorswift13," as actress/director Elizabeth Banks, model Lily Aldridge, and comedienne Ellen DeGeneres also showered Swift with birthday love online.