Sundbyfoss is a village in Holmestrand Municipality in Vestfold county, Norway. The village is located along the lake Hillestadvannet, about 3 kilometres (1.9 mi) south of the village of Hof. The village of Gullhaug lies about 7 kilometres (4.3 mi) to the southeast and the town of Holmestrand lies about 10 kilometres (6.2 mi) to the southeast. The village of Hvittingfoss in Kongsberg Municipality lies about 8 kilometres (5.0 mi) to the west. Hillestad Church lies about 3 kilometres (1.9 mi) east of the village.