1859 In early 1859, Captain W. F. Raynolds was directed by the War Department to organize an expedition to explore the Yellowstone River and the Missouri River. During 1859, the party traveled up the Missouri River and into what would become northeastern Wyoming. Between October 12 and 17, they searched for and located their winter headquarters at Deer Creek, near present Glenrock, Wyoming. They would remain there until May of 1860, then travel west and north to the Yellowstone country.
1882 Theresa Post Office was established on October 17, 1882 in Albany County prior to the formation of Converse County. At the time of the establishment of the post office in 1882, the local name for the location was Brown Springs.