An "extremely cooperative" Lohan was booked into Lynwood correctional facility shortly after 10:00 am (1700 GMT) on Tuesday, Los Angeles County Sheriff's Department spokesman Steve Whitmore told reporters.
But no sooner had she donned jail garb and been put behind bars in a nine-square-meter (98-square-foot) cell than Whitmore said the actress's sentence would be reduced to just 14 days, with her release set for August 2.
Lohan, 24, was whisked without comment into a Beverly Hills courtroom, where she was put in handcuffs and transported to Lynwood to begin her sentence for violating parole after a 2007 drunk driving conviction.
TV helicopters chased the police car taking the actress and model, who was dressed in jeans and a black leather jacket, before she finally disappeared through the gates of the correctional facility at Lynwood, in the southern outskirts of Los Angeles.
Media scrums and supporters were also at the court where Lohan appeared before Judge Marsha Revel to report for her sentence.
She was accompanied by her lawyer Shawn Chapman Holley, rather than attorney to the stars Robert Shapiro, as had been expected.
"We love you Lindsay!" her father, Michael Lohan, shouted out. One fan bore a T-shirt with Lohan's picture and the inscription "Linnocent." Others threw gold confetti in her path.
Revel took little time on the formalities of confirming the 90-day sentence she imposed July 6 for Lohan's parole violation following the 2007 DUI conviction.
Lohan had been convicted of missing seven classes of a mandatory 90-day, in-patient substance abuse program.
While she broke down in tears at that earlier court appearance, Lohan seemed composed and resigned on Tuesday.
Life in the Century Regional Detention Facility will have none of the luxuries usually available to Lohan, who began as a child actress and was considered a serious star in the making before becoming known chiefly for substance abuse, partying and appearances in the tabloids.
Paris Hilton is among other celebrities who have been incarcerated at the Lynwood prison and experts said wardens would carefully protect Lohan from the kind of violence common behind bars.
"People with notoriety are kept away" from the general jail population for security purposes, said Whitmore.
Authorities had said her actual time served could be as little as one-fourth of the sentence, given California's massive jail overcrowding and the relatively minor nature of her infractions.
Provided she behaves in prison, she'll be out well ahead of the September premier of her latest movie, the action thriller "Machete."
Lohan, who starred in the 1998 film "The Parent Trap" and 2003's "Freaky Friday," was arrested in May 2007 after crashing her Mercedes in Beverly Hills.
After a stay in rehab, the star of "Mean Girls" and other hit films was caught two months later for drunk driving and cocaine possession. At the time, she spent a mere 84 minutes in jail.
The latest calamity for Lohan did not dent the enthusiasm of fans who remember her for a series of promising roles and celeb-page glamor.
"I'm here because Lindsay deserves the support of everyone," Hollywood autograph hunter Jake Byrd said.