The controversial author posted a picture of the threat that featured her family’s address - that she blacked out, an image of a pipe bomb and a bomb-making handbook.
The threat was posted by an alleged Irish account using the name: ‘Shane@fuckfinegael’
The Harry Potter writer said the account “remains active, naturally” and added the hashtag #BeKind.
However, the account has since been shut down.
There were numerous responses supporting the author with one writing: “It's gone, but we all know who he is, so a little visit from the local gardai would be appropriate.”
One person added: “Another example of why women need online female-only spaces.”
Another added: “I’m so sorry that you have to deal with this. There are so many people who support you and are so grateful for you.”
One fan said: “Standing with JK Rowling from Australia…you’ve brought much happiness to my nephews and nieces.”
“I’m so sorry this is happening, Jo,” another added.
“Thank you for continuing to speak out for women’s rights and for publicly supporting vulnerable groups. It means the world to so many. I live not far from you and will keep my eyes peeled for any suspicious activity. Much love.”
One person added that this is: “So desperately sad that this is happening to you and your family. I hope you can hang onto the knowledge that millions around the world thank you from the bottom of our hearts, not only for your wonderful writing but for standing up for the rights of women and girls.”
One said: “I don’t agree with anything you say or stand for. However, this is not ok.”
Another said: “Can’t imagine how it feels to face this bombardment of vile threats all the damn time. Thank God that there are millions and millions who think the world of you and believe you to be an absolute inspiration. Hope that in some way compensates.”
Actor James Dreyfus branded it "more frightening, repellent, dangerous behaviour” aimed at Ms Rowling, while Scottish broadcaster Muriel Gray said in support of the author: "You, and your family, remain amongst the kindest humans I know.”
Barrister Allison Bailey blasted the tweet as “a threat to kill – it is one of the many that JKR & other women face for the crime of supporting women’s rights”.
Additionally, an account called “JKR’s Barmy Book Army” called it an “absolute disgrace”, while another said about the writer of the offending tweet: "Hope they are charged and have the book thrown at them”.
It is the latest example of “doxxing” – revealing personal information about someone online – that JK Rowling has suffered after after a trio of trans activists in November posted an image outside her home where her address could clearly be seen.
They were holding signs reading “Don’t be a cissy”, “Trans liberation now”, and “Trans rights are human rights”.
Rowling revealed at the time how she and other women who had spoken out on gender issues had received "so many death threats I could paper the house with them".
She vowed that would not be silenced despite "campaigns of intimidation", stalking and harassment, adding that "families have been put into a state of fear and distress" by transgender activists.
"Perhaps... the best way to prove your movement isn't a threat to women, is to stop stalking, harassing and threatening us,” she said at the time.
Rowling has been involved in a simmering row with the transgender community over her belief that women's sex-based rights should be protected.
The dispute began around two years ago when the author tweeted against use of the phrase "people who menstruate", rather than only women.
The message caused a rift with some of the stars of the ‘Harry Potter’ movies, including lead actor Daniel Radcliffe, who tweeted an apology on her behalf.
"Transgender women are women," Radcliffe wrote in a post.
Rowling said she had been "appalled" to hear from various women who had spoken out on transgender issues, including those with no public profile, and suffered abuse including threats of rape.
"None of these women are protected in the way I am," she said, attacking the "socio-political concept of gender identity" as opposed to biological sex.