It is not clear how many Federation-Cardassian Treaties have been signed.
Since the Federation-Cardassian War ended with a truce some time in the late 2350s or early 2360s there must have been some sort of agreement. However, the most famous and far-reaching treaty was signed in 2370.
The Federation-Cardassian Treaty of 2370
This treaty was supposed to be the final end to the hostilities of the war. Primarily negotiated by Admiral Alynna Nechayev, it mainly dealt with the status of the Federation-Cardassian border and led to the establishment of the Demilitarized Zone.
Within the Zone, neither side was permitted to deploy armaments, or establish military bases. The official border, which ran through the zone, was redrawn requiring the exchange of several worlds. Although the colonists on these worlds were given the option of resettlement, many refused as they felt that their rights had been ignored. The resulting dissatisfaction eventually led to the establishment of the Maquis.
After the annexation of the Cardassian Union by the Dominion the treaty was effectively void. Any further negotiations between the Federation and the Cardassians would have been carried out as part of the Dominion War peace treaty.