Ōkubo Tadamasu (大久保 忠増, 1656 – September 14, 1713) was daimyō of Odawara Domain in Sagami Province, (modern-day Kanagawa Prefecture) in early Edo period Japan.
On October 4, 1707, the Great Hoei earthquake again devastated Edo and Odawara, destroying much of what had been rebuilt from the earlier disaster.
This was followed by the Hōei eruption of Mount Fuji in December, with volcanic ash raining on Edo and Odawara and repeated earthquakes.
The following year the Sakawa River flooded due to sediment build-up resulting from the ash fall, and the crops failed.
Tadamasu appealed to the Tokugawa shogunate for assistance, and in response, the government annexed the disaster-struck portions of his territories as tenryō under the direct control of the central government, and provided Tadamasu for new territories with an assessed value of 60,000 koku scattered across the provinces of Izu, Mimasaka and Harima.