Osea Island is part of the Hundred of Thurstable, a name which probably derives from the pagan deity Thunor. This is the Anglo-Saxon name for Thor. The neighbouring island, Northey, was in a different hundred, probably because the causeways to the two islands lead to opposite shores of the Blackwater estuary. The Domesday Book gives the following information about Thurstable, Osea and Northey islands:
"Hundred of Thurstable: Richard holds (Great) Totham from Hamo, which Thorbert held as one manor, for 5 hides before 1066. Then 10 villagers, now 9: always 16 smallholders. Then 12 slaves, now 13. Then 4 ploughs in lordship, now 3. Always 5 men's ploughs.
Woodland: 100 pigs; meadows, 16 acres; 2 salt-houses. Always 20 cattle; 40 pigs. Then 5 cobs, now 2; then 100 sheep; now 150; always 40 goats. Value then and later 100s; now £6.
In the same (totham) 8 free men held 1 1/2 hides which Richard also holds. Always 2 ploughs. Meadow, 3 acres. Value 20s.
He also holds Osea (Island), which Thorbert held before 1066 as a manor, for 4 hides. Then 1 smallholder, now none; always 3 slaves. 1 fishery; pasture, 60 sheep. Value 60s.
Hundred of Wibertsherne: Richard holds Northey Island from Hamo (a steward) which Thorbern, a free man, held before 1066 as a manor, for 4 hids and 40 acres.
Then 2 villagers, now 3. Always 4 slaves; 2 ploughs in lordship; 1 men's plough. Pasture, 60 sheep. Value then 60s, now £4."
Osea and Northey Islands, as they are today. The sea was about a metre lower in the 9th century, so the islands would have been larger. [1]