YouTuber 'Adam the Woo' Dead at 51

YouTube star Adam the Woo has died ... TMZ has learned.

A spokeswoman for Osceola County Sheriff's Office tells TMZ ... deputies were first dispatched to Adam's home outside Orlando, FL around 12:24 PM Monday for a well being check. We're told the home was secured, but deputies were unable to make contact with the adult male who lived there.

The Sheriff's Office tells us deputies returned to the address later in the afternoon around 2:53 PM after receiving a call for an unattended death. Authorities say a friend became concerned, borrowed a ladder, and looked through a third story window, where he saw Adam lying on a bed not moving.

Deputies entered the residence alongside Fire Rescue, and Adam pronounced deceased inside the home. The medical examiner will conduct an autopsy to determine the cause of death.

Investigators say the friend who discovered him had seen Adam the day before. Authorities also tell us they notifies Adam's father, who lives locally about his death.

Adam the Woo rose to fame through his popular YouTube channel, where he documented travel, theme parks, roadside attractions, and pop-culture locations ... growing a massive following over the years.

Adam was 51.