Tadeusz Kościuszko monument, Monument and cenotaph in Montigny-sur-Loing, France.

The Tadeusz Kościuszko monument is a chapel and burial memorial featuring a vaulted underground crypt beneath an earthen mound. A medallion sculpted by Leplat adorns the exterior of the structure.

Frantz Zeltner, son of the Swiss minister Peter Josef Zeltner who hosted Kościuszko at Berville, gave the land at Sorques, and a first monument was built there on 9 October 1836 by villagers as a five-foot mound. Its chapel Saint-Thadée was inaugurated on 3 September 1837 before some ten thousand people, prompting the Russian ambassador to complain to Louis-Philippe. The mound was razed at the end of the 19th century; the present chapel, by architect Fernand Lucas, dates from 1924.

Locals call Montigny-sur-Loing "Polonia-sur-Loing", a nickname earned when thousands gathered here on 3 September 1837 for the inauguration of a chapel dedicated to Saint Thaddeus, Kościuszko's patron. The Russian ambassador protested to King Louis-Philippe, who banned the celebrations. Annual ceremonies have since drawn Polish delegations, including in 1917, 1967, 2018 and 2019.

The monument stands on the north side of departmental road 148, the Fontainebleau–Treuzy-Levelay road, at the entrance to the Sorques hamlet, near the perpendicular Larchant road. The entrance door opens onto the road, and a metal fence protects it. The vaulted crypt beneath the tumulus has collapsed, so the interior is not visitable.

The bronze medallion above the door was made by the sculptor Leplat after a model by David d'Angers and fixed to the rebuilt chapel in 1924. The vaulted crypt dug under the tumulus has since collapsed, so the door now opens onto a sealed space.