Riley Strain's death is not the fault of the bars that served him while he was clearly intoxicated ... so says the Tennessee Alcoholic Beverage Commission.

The TABC released its findings Thursday after a months-long investigation, and it says it found no clear evidence via eyewitnesses, interviews, or camera footage to suggest bartenders served him booze while he was visibly drunk.

TABC lays out the timeline of the night in detail, according to several of Riley's fraternity brothers ... who say the group went from Miranda Lambert's bar to Garth Brooks' place before walking into Luke Bryan's for the first time.

After hanging there for a bit, they went to Kid Rock's place, but then decided to go back to Luke Bryan's. One of Riley's frat bros told investigators by that point Riley had consumed at least 7 drinks, and was slurring his speech ... so they got him 2 waters.

According to the report, Riley tried to close out a tab -- which he didn't actually have -- and the bartender then told security to eject him from the bar.

TABC says Strain remained stable on his feet at all 4 places the group visited ... so, ultimately the commission says it doesn't look like the bars overserved him.

Of course, we know how the rest of the tragedy played out. Riley left the bar, and surveillance video captured him walking through the streets, sometimes with a normal gait and at other times stumbling around the sidewalk.

Ultimately, Riley's body was found washed up at a concrete plant near the Cumberland River several weeks after he went missing. The coroner has ruled his death accidental by drowning and ethanol intoxication.

Riley's family has repeatedly cast doubt on the manner of his death, and also blasted his frat brothers for letting him leave Luke Bryan's alone.

In any case, seems the state's saying the bars aren't at fault in this tragedy.