Maria Eleonora I Boncompagni
Maria Eleonora I Boncompagni (1686–1745) was the Princess of Piombino, Marchioness of Populonia, Princess of Venosa and Countess of Conza, Lady di Scarlino, Populonia, Vignale, Abbadia del Fango, Suvereto, Buriano, Cerboli e Palmaiolan, and Lady princess of the Tuscan Archipelago including the islands of Elba, Montecristo, Pianosa, Gorgona, Capraia, and Isola del Giglio, from 1733 until her death.

Biography 
She was the oldest of six daughters to her mother Ippolita Ludovisi and father Gregorio II Boncompagni. She succeeded her mother as sovereign at her death in 1733. 

She was married to her uncle, Don Antonio I Boncompagni (1658–1731), VI Duke of Sora, who became Prince of Piombino by the right of his wife. 
They had 5 children :
Maria Olimpia (1703-05), 
Niccolo (1704-09), 
Francesca Cecilia (1705-75), married Francesco Maria Carafa, IV principe di Belvedere, 
Gaetano (1706-1777), their successor, 
Pietro Gregorio (1709-1747), married Maria Francesca Ottoboni, II Duchess of Fiano.

References
 Mauro Carrara, Signori e principi di Piombino, Bandecchi & Vivaldi, Pontedera 1996.
http://www.guide2womenleaders.com/womeninpower/Womeninpower1700.htm

1686 births
1745 deaths
Princes of Piombino
18th-century Italian nobility
18th-century women monarchs
17th-century Italian women
18th-century Italian women