Born in South Carolina, Thompson moved to Kaskaskia in southern Illinois as a young man and lived in the area for the rest of his life, working primarily as a surveyor.

In addition to his surveying work, he served in various positions such as probate judge, county commissioner, and officer in the Illinois militia during the Black Hawk War.

Thompson's plat fixed the location associated with the word "Chicago", which had previously been used for various places around the southwestern shore of Lake Michigan, and allowed the residents of the area to obtain legal title to their property.

Thompson served as a teacher in Kaskaskia for three years before marrying his cousin Margaret in October 1817 and thereafter living in nearby Preston.

[7] It did not extend to Lake Michigan because Fort Dearborn, which had been built by the United States government in 1803, occupied land on the lakeshore.

[6] The pioneer Mark Beaubien's cabin ended up in the middle of one of the streets; he bought two lots of the plat and moved his property by a couple of yards.

[8] In this capacity Thompson dealt with the estates of early Illinois politicians such as Shadrach Bond and Pierre Menard.

[2] By 1859 he had become Deputy Surveyor of Randolph County,[9] at which point his reputation was such that "whenever the name of James Thompson is mentioned, the idea of surveying is suggested.

[11] Jean Baptiste Point du Sable was the first non-indigenous permanent resident of the area, settling at the mouth of the Chicago River no later than 1790.

[12] The United States government built Fort Dearborn in the area in 1803,[13] and more pioneers settled in the early 19th century, numbering approximately 75 by 1830.

[15] Thompson's plat created a grid system for Chicago's street layout,[16] and gave its residents legal title to their land.

[20] The intersection of State and Madison Streets was selected as the origin of Chicago's address system in 1909 because they were the baseline of Thompson's plat.