Jenny's locket was a locket belonging to Jenny Wilder.
The locket held a picture of her dead father and was very precious to her because it was the last bit of her father that she had left, aside from what she carried on the inside. Once while swimming in a lake of the Walnut Grove area with her friends, she lost the locket at the bottom of the lake. Unfortunately, Jenny's determination to get it back nearly cost her life as she had become entangled on something at the bottom of the lake, and could not get back up in time before lapsing into unconsciousness before being rescued. Being without oxygen for too long, she suffered minor brain damage and had to be closely looked after by her adoptive parents Laura and Almanzo Wilder and a kind elderly but retired doctor, who helped her get better. (Episode 912: Marvin's Garden)