Youngbloods Frontman Jesse Colin Young Dead at 83

3:17 PM PT -- The Aiken County Coroner in South Carolina tells TMZ ... Jesse Colin Young was at his home sometime before 3 PM ET Sunday when an unspecified event happened, and emergency medical services were called ... paramedics transported Young to a hospital, where he was pronounced dead at 3:13 PM. The coroner said Jesse's death was natural, but there's no official confirmation yet on his cause of death.

Jesse Colin Young, a singer known for his work with the Youngbloods, is dead.

The singer/songwriter died Sunday afternoon in Aiken, South Carolina ... according to his wife and manager, Connie Young. The cause of death is unclear.

Jesse is best known for providing vocals on the Youngbloods' 1960s hit song "Get Together" ... an international anthem calling for brotherhood and peace.

In addition to his time with the Youngbloods, Jesse also launched a solo career ... playing the guitar and singing socially conscious lyrics on a slew of solo albums.

Jesse blended folk, blues, jazz and country with some rock and roll ... and he had his hands on all facets of the music industry ... he was a songwriter, singer, instrumentalist, producer and label owner.

In recent years, Jesse hosted a podcast ... and he was always an activist for social and environmental issues, as a product of the 1960s hippie counterculture era.

Jesse was 83.