The community includes an historic marker claiming it to be a French mission and trading post in 1673, which would make it the oldest European settlement in Indiana as well as in neighboring Illinois.

[1] The earlier existence of an Indian village and a French trading post are identified by an historic marker in Tassinong.

The earliest presence of Europeans in the Porter County area is in 1679, when Sieur de La Salle passed down the Kankakee River, 7 miles (11 km) to the south.

[2] At that time, the area south of Lake Michigan was embroiled in the Beaver Wars, which began in the Iroquois lands of New York in 1638.

[9] The decline of the village began in 1865 when the Pittsburgh, Cincinnati and St. Louis Railroad was built through Kouts, two miles (3.2 km) to the south.

[10] The location of Tassinong first appeared on a map in 1875, when the state of Indiana completed its survey of Morgan and Pleasant townships in Porter County.

[12] The oldest available Atlas of Porter County, 1876, shows the village of Tassinong in the southeast quarter of Section 31, Township 34, Range 5.

[16] The Kouts High School History of Pleasant Township was published in the local paper in 1936, establishing the presence of Claude-Jean Allouez, Claude Dablon, Father Jacques Marquette, and René-Robert Cavelier, Sieur de La Salle in Porter County, passing "through this territory on foot".

He identified that Fathers Allouez, Chardon, and D’Ablon (Dablon) preached at Tassinong and that, in 1875, Sylvester Pierre, the Tassinong postmaster provided an extensive history for the village, including that it was originally called Sequada Tiera by the Spanish, and then Haute Terre by the French.