| Native Name: | 吉井藩 |
| Conventional Long Name: | Yoshii Domain |
| Common Name: | Yoshii Domain |
| Subdivision: | Domain |
| Nation: | Japan |
| Government Type: | Daimyō |
| P1: | Kōzuke Province |
| S1: | Prefectures of Japan#Former prefecturesIwahana Prefecture |
| Today: | Gunma Prefecture |
| Year Start: | 1590 |
| Year End: | 1869 |
| Life Span: | 1590–1610 1682–1698 1709–1869 |
| Era: | Edo period |
was a feudal domain under the Tokugawa shogunate of Edo period Japan, located in Kōzuke Province (modern-day Gunma Prefecture), Japan. It was centered on Yoshii jin'ya in what is now part of the city of Takasaki, Gunma. Yoshii was ruled through much of its history by a branch of the Takatsukasa clan, which had adopted the patronym of Matsudaira.
After Tokugawa Ieyasu took control over the Kantō region in 1590, he assigned one of his generals, Sugawara Sadatoshi, the 20,000 koku holding of Yoshii. Sadatoshi laid out the foundations of a town and market, and was succeeded by his adopted son, Okudaira Tadamasa in 1602. Tadamasa’s mother was the eldest daughter of Tokugawa Ieyasu; he was transferred to Kanō Domain in 1610. The domain then became vacant and was ruled as a hatamoto holding until 1682.
In 1682, Hotta Masayasu, a hatamoto bureaucrat in the Tokugawa shogunate, passed the 10,000 koku mark and was raised in status to daimyō. Yoshii Domain was revived to be his seat, but he was transferred to Omi-Miyagawa domain, where his descendants resided to the Meiji restoration, and Yoshii again reverted to tenryō status.
Likewise, in 1709, the hatamoto Matsudaira Nobukiyo attained the 10,000 koku mark, and Yoshii Domain was revived as his seat. Nobukiyo was the grandson of the kuge Takatsukasa Nobuhira, whose sister married Shōgun Tokugawa Iemitsu. He traveled to Edo with only one retainer, but was awarded estates and servants and eventually married a daughter of Tokugawa Yorinobu and adopted the Matsudaira name. The descendants of Matsudaira Nobukiyo continued to rule Yoshii until the end of the Edo period.
During the Bakumatsu period, the final daimyō, Matsudaira Nobunori, changed his name to Yoshii Nobunori, and joined the new Meiji government in February 1868. With the abolition of the han system in July 1871, Yoshii Domain became part of “Iwahana Prefecture”, which later became part of Gunma Prefecture.
As with most domains in the han system, Yoshii Domain consisted of several discontinuous territories calculated to provide the assigned kokudaka, based on periodic cadastral surveys and projected agricultural yields.[1] [2]
| Name | Tenure | Courtesy title | Court Rank | kokudaka | |
| Suganuma clan (Fudai) 1590-1610 | |||||
| 1 | 1590–1602 | Daizen-no-suke (大膳亮) | Lower 5th (従五 位下) | 20,000 koku | |
| 2 | 1602–1610 | Hida-no-kami (飛騨守) | Lower 5th (従五 位下) | 20,000 koku | |
| tenryō 1610-1682 | |||||
| Hotta clan (fudai) 1682-1693 | |||||
| 1 | 1682–1693 | Buzen-no-kami (豊前守) | Lower 5th (従五位下) | 10,000 koku | |
| tenryō 1693-1709 | |||||
| Takatsukasa-Matsudaira clan (shimpan) 1709-1871 | |||||
| 1 | 1709–1724 | Echizen-no-kami(越前守); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 2 | 1724–1760 | Echizen-no-kami(越前守); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 3 | 1760–1771 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 4 | 1771–1775 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 5 | 1775–1800 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 6 | 1800–1803 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 7 | 1803–1841 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 8 | 1841–1847 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |
| 9 | 1847–1865 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 5th (従五位下) | 10,000 koku | |
| 10 | 1865–1871 | Sahyōe-no-kami (左兵衛督); Jijū (侍従) | Lower 4th (従四位下) | 10,000 koku | |