The Nothing Compares To You singer had been reported missing since Sunday.
Police in Cook County, Illinois, were alerted after she went on a bike ride at 06:00 local time on Sunday, and did not return.
Wilmette Police told the BBC she had been located, after earlier saying they were “seeking to check the well-being” of the 49-year-old.
Fears for the singer grew as she was deemed a possible suicide risk.
Scroll down to read O’Connor’s latest Facebook post…
O’Connor has had her fair share of troubles in the past year. She has spoken openly about her mental health problems, often taking to social media to speak directly to her fans and the public.
In 2015, she cancelled a string of summer dates, because she was from exhaustion “due to an existing not resolved medical situation”, according to a statement from her management.
A week later she posted a shocking revelation about her son on Facebook, writing ““My child has been suffering with a life-threatening medical condition since early March 2015.”
After news of her disappearance broke, some of the reaction on Twitter and social media was criticised for showing a lack of understanding about mental health.
Loads online, being harsh on Sinead O Connor.That’s often the face of mental health issues for lots of people. It’s not nice to be around.
— Rubber Bandits (@Rubberbandits) 16 May 2016
Wilmette Police issued a statement saying the singer “is no longer considered a missing/endangered person”.
Accoring to the Chicago Tribune Deputy Chief Kyle Perkins said that police would not hold a press conference, and no further information about the incident would be released.
It is believed that the singer was hospitalised after she was found.
At around 3am this morning (GMT) O’Connor posted a fiery open letter to her ex-husband Irish writer John Reynolds on Facebook. It reads:
You tell that evil son of ours that a person who suffers from two f*****g medical conditions of which the symptoms include suicidal compulsion isn’t being manipulative if while he is being a f*****g chauvinist bully like his grandfather they say they’re going to or feel like killing themselves. You all abandoned me FOR BEING SUICIDAL.
The strongly-worded letter goes on to talk about killing herself and addresses her children and her financial troubles.
The singer says she will sue her ex-husband, saying she has not been able to work and that he has been “sending me the bills for twenty f*****g grand every three months.”
O’Connor has four children, Jake, Shane, Roisin, and Yeshua.
I will see you all in court. I want damages. I have been unable to work. I have lost last year’s income and this year’s. I have had enormous medical expenses, and enormous trauma because of your torturing of me.
The letter is signed Sinead Marie-Bernarde Aoibheann O’Connor.