A cooling board is a board used to present a dead body. In winter months it would be difficult to bury the dead due to the earth being frozen, so the body is wrapped and propped in a barn

Barn

A barn is an agricultural building used for storage and as a covered workplace. It may sometimes be used to house livestock or to store farming vehicles and equipment...

 until the ground thaws out. Referred to in a number of Blues

Blues

Blues is the name given to both a musical form and a music genre that originated in African-American communities of primarily the "Deep South" of the United States at the end of the 19th century from spirituals, work songs, field hollers, shouts and chants, and rhymed simple narrative ballads...

 songs, for example by Blind Willie McTell

Blind Willie McTell

Blind Willie McTell , was an influential Piedmont and ragtime blues singer and guitarist. He played with a fluid, syncopated fingerstyle guitar technique, common among many exponents of Piedmont blues, although, unlike his contemporaries, he used exclusively a twelve-string guitar...

:http://www.harptab.com/lyrics/ly2736.shtml.

Son House

Son House

Eddie James "Son" House, Jr. was an American blues singer and guitarist. House pioneered an innovative style featuring strong, repetitive rhythms, often played with the aid of slide guitar, and his singing often incorporated elements of southern gospel and spiritual music...

 also makes a reference to a cooling board in his well known song Death Letter

Death Letter

"Death Letter", also known as "Death Letter Blues", is the signature song of the Delta blues musician Son House. It is structured upon House's earlier recording "My Black Mama, Part 2" from 1930...

.

"So, I grabbed up my suitcase, and took off down the road.
When I got there she was layin on a coolin' board."

Also found in a song by the late Donnie Hathaway:http://www.lyricsbox.com/donny-hathaway-lyrics-thank-you-master-for-my-soul-dmwlvqr.html

"'cause the walls of my room was not the walls of my grave
my bed was not my cooling board (y'all don't know what i'm talkin' 'bout)"

Benjamin B. French witnessed Abraham Lincoln's remains, after transfer from the Peterson House to the White House, being "taken from the box in which they were enclosed, all limp and warm, and laid upon the floor, and then stretched upon the cooling board."