Castelnuovo della Misericordia is the result of a complex housing process that characterized the hilly area in the Middle Ages: several castles, many of which no longer exist, followed each other and partly coexisted, including Camaiano, Castelvecchio, and Castelnuovo.
Developed at the foot of the latter, today's hamlet also includes the remains of Castelvecchio, which was largely destroyed by a devastating earthquake in 1846. The name ‘della Misericordia’ derives from Pia Casa di Misericordia of Pisa, which owned a large estate grazed by animals since the fourteenth century and whose administrative center was the building known as 'Villa Santa Maria Assunta' (or Fattoria di Castello).
The original parish of Santo Stefano, included in the walls of the castle, was replaced by the present church, built in a more central position in the mid-seventeenth century.
Its municipality was independent for a long time and was united to Rosignano Marittimo only in 1776.
The surroundings of the town offer rural and wooded landscapes of rare beauty, which can be crossed thanks to the close network of ancient trails rich in archaeological remains, such as the Etruscan necropolis of Pian dei Lupi and the surrounding wall of Monte Carvoli.