The following information was taken from the film The Ring, as well as documents appearing on ring-themovie.com and the now-defunct promotional website The Morgan Ranch. Special thanks go to mikejonas for writing and compiling the initial draft of this timeline and its notes.

1963

May 8th
Under the care of Dr. Deever at Eola County Psychiatric Hospital (ECPH), Anna Morgan conceives her first child. She miscarries a few months later, and will miscarry several more times.

1970-77

Strange things happen on the island; the harvests are lean, the catches are small. At the Morgan Ranch, Samara's powers (which appear to be growing with time) are slowly but surely driving her mother insane.

1977

July 17th
Samara is admitted to ECPH, where it becomes apparent that she is no ordinary girl. Besides having "severly impaired" judgement and being completely insensitive to pain, she also possesses the ability to project mental images onto film. This ability is labelled projected thermography, and is studied at some length by ECPH employee Dr. Scott. At some point during her stay, Samara will undergo a "failed psychosurgery" and be heavily medicated "for staff's safety." This would indicate that it is suspected, if not feared, that Samara had some hand in Dr. Scott's untimely death.

1978

February
Anna is treated at ECPH for depression and suicidal thoughts.

February 23rd
Samara's sessions are terminated at her father's request. Later, against doctors' protests, Richard checks Samara and Anna out of ECPH and takes them back to Moesko Island. He then locks Samara in the barn.

September 7th
The horses at the Morgan Ranch begin killing themselves. A town meeting is held when the death toll rises to 15.

September 20th
Officials remain stumped. "Equine Tests Negative," one newspaper headline reads. By now at least 27 horses have killed themselves. Before the end of the month, Anna is readmitted to ECPH.

October 15th
The Morgan Ranch is quarantined, and will remain so for at least five weeks. A team from the University of Washington headed up by Dr. Morrow arrives on the scene. They are stymied when results turn up negative. "We're back to square one," Morrow laments. "Bizarre and unconfirmed rumors" about the cause of the epidemic float around the island.

October 20th
Anna is released from ECPH.

The Morgans take Samara to Shelter Mountain, where Anna suffocates her and throws her into the well. Anna kills herself, and the behavior of the horses soon returns to normal. The inhabitants of Moesko Island believe Samara was sent back to ECPH.

notes

-One of Samara's diagnoses is dated October 5th, 1978. This would indicate either a discrepancy in the timeline, or the fact that she continues to affect both Anna and the horses over long distance.

-Anna's obituary says she was under the care of ECPH for the two years before her death. Does that mean she was at ECPH all that time? Probably not, since she seems to have been around at the time of the horses' deaths. She (and presumably Samara as well, following her release) was probably just making regular visits to the facility for treatment.

-The articles about the horse suicides point out that the deaths happened within a five-week span of time, and ended almost immediately after Anna's suicide (by the time Anna kills herself, the investigation into the deaths had lasted "several months"). If Samara had been in the barn most of her life, she probably would've killed the horses earlier (unless -- and this is also a valid explanation -- she hadn't refined her abilities until then); so it's likely that she wasn't put into the barn until shortly before making the horses kill themselves.

Since all this happens within a year of Samara's release (which, according to the documents, happened around the time of her eighth birthday), one would think that Richard checked Samara out of ECPH with some idea of what he was going to do with her, i.e. keep her on the island away from the public eye. He would also keep her away from Anna in the hope that some distance will alleviate Anna's symptoms. Thus, Samara was put in the barn soon after their return to Moesko Island.

Keeping this in mind, it's more than likely that these events -- the release from the hospital, the banishment to the barn, the death of the horses, Samara's murder, and Anna's suicide -- all happened in immediate, consecutive order and within a short period of time, perhaps as little as five or six weeks.

-None of this contradicts anything in the movie, but it makes the timeline a little murkier. One could posit that Richard had checked Samara out of ECPH earlier in the year (the day after her birthday, according to a clipping on themorganranch.com), and sometime later stuck her in the barn, where she eventually drove the horses mad. The horses stopped dying after Anna was readmitted to ECPH, but that didn't stop the authorities from quarantining the ranch to investigate the cause of the horses' death. The articles also say that the horses continued to behave oddly (though it doesn't say they killed themselves) until Anna's suicide shortly after throwing Samara into the well.