Jezioro Białe, Gostynin County, a lake in Masovian Voivodeship, in Gostynin County
As the oldest son Siemowit obtained the central part of Masovia, with Rawa Mazowiecka (capital) Sochaczew, Zakroczym, Gostynin, Ciechanów and Wizna.
Siemowit V (also spelled Ziemowit; 1389 – 16 February 1442) was from 1426-1434 a Prince of Masovia in Rawa, Plock, Sochaczew, Gostynin, Płońsk, Wizna and Belz i.e., hereditary vassal Polish, the breakdown in 1434 goes as follows; prince of Rawa, Gostynin and Sochaczew.
Between 1679 and 1681, he acquired lands near Iłów comprising one town and 10 villages, in the counties of Gostynin and Sochaczew.