The passage of the Land Ordinance of 1785 created the rectangular survey system for the mapping and subsequent sale of the western public lands of the United States. In 1803, the first survey of the lands, which would later become the state of Illinois, began. After moving northwards from southern Illinois in 1806, the federal surveyors finished surveying the last townships in 1843, but for four decades afterwards, the General Land Office continue to conduct occasional surveys of areas in the state such as islands and lakes. The Illinois State Archives, working together with the Illinois Secretary of State and the Department of Information Technology, have brought all of these township plats online for public consideration and research purposes. The 3,457 hand drawn maps available are valuable repositories of information about the six miles square townships, often including information about existing natural features and, in some cases, man-made features as well. Along with the plat maps themselves, the site also contains essays about the surveyor's work, the equipment they used, and potential surveying problems they often encountered.