From peaceful + -ness.

peacefulness (uncountable)

1. The state of being peaceful.
   • 1892, Elijah P. Brown, Blasts from a Ram's Horn, page 238:

     His trust in God was exemplified in his constant peacefulness and freedom from all concern on the question of supplies, no matter how unassuring the outlook happened to be.

• tranquillity
• See also Thesaurus:calmness

• peace
• peaceful