The Deadose (Agdoza, Doxsa, Igodosa, Jacdoas, Judosa, Yacdossa) Indians are known to have existed only during the eighteenth century. It is now clear that they were closely related to the Bidais and spoke an Atakapan language. In the early eighteenth century they lived between the junction of the Angelina and Neches rivers and the upper end of Galveston Bay. Some time after 1720 the Deadoses moved westward to an area lying between the Brazos and Trinity rivers in the vicinity of present Leon, Madison, and Robertson counties. Between 1749 and 1751 the Deadose Indians, along with other Atakapan-speaking groups (Akokisas, Bidais, and Patiris), were represented at the short-lived San Ildefonso Mission near present Rockdale in Milam County. A few Deadose (Yacdossa) Indians entered San Antonio de Valero Mission shortly afterward. In the second half of the eighteenth century the Deadoses were at times closely associated with certain Tonkawan groups (Ervipiames, Mayeyes, and Yojuanes), and it was once thought that their language might have been Tonkawan. This view was abandoned because other evidence clearly indicated an Atakapan linguistic affiliation. The Deadose Indians suffered heavily from European-introduced diseases, especially measles and smallpox, and they eventually lost their ethnic identity in the latter part of the eighteenth century. Remnants of the Deadoses probably joined the Bidais, who survived into the nineteenth century, although some may have been absorbed by the Tonkawas. J. R. Swanton erred in identifying the Yacdossa of San Antonio de Valero Mission as Coahuiltecans.