 After the War of 1812 , the first Europeans in the area were French settlers loyal to the British Crown who moved north from Detroit . They successfully traded with the Three Fires Confederacy , which contributed to the growth of the area . After its foundation , Port Sarnia expanded throughout the 19th Century ; on 19 June 1856 , the residents passed the Act to <unk> the Town of Sarnia and the name Port Sarnia was officially changed to Sarnia effective 1 January 1857 . The Act mentioned 1 @,@ 000 inhabitants in three wards . The wealth of adjoining stands of timber , the discovery of oil in nearby Oil Springs in 1858 by James Miller Williams , and the arrival of the Great Western Railway in 1858 and the Grand Trunk Railway in 1859 all stimulated Sarnia 's growth . The rail lines were later linked directly to the United States by the opening of the St. Clair Tunnel under the St. Clair River at Sarnia in 1890 , by the Grand Trunk Railway , which was the first railroad tunnel ever constructed under a river . The tunnel was an engineering <unk> in its day , achieved through the development of original techniques for excavating in a compressed air environment . 
