It was difficult to get hard numbers for Paraguayan deaths in the war. Paraguay had no accurate census, so any population numbers are an estimate. And they probably didn’t have an accurate number of war deaths.
But the population was badly hit by the war, especially for young men. The crisis after the war was so acute, however, that the country legalized polygamy for a few years after the war because there were so few men alive.
Paraguay also lost a lot of people people in the Chaco War of 1932-35, and they won that one (35-50K out of about 800K – though some estimates go up to 100K when civilians are included).
Are we just figuring this as in number (or percentage) of troops/population killed, and still lost the war, or are we taking other stuff into account, too? (Like: defeated; a few cities razed; your country occupied and/or split up by victors; most of leadership dead, executed, or imprisoned, and your new constitution says that you renounce war forever?)