The noun populace can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be populace.

How do you use populace?

(1) The populace at large is / are opposed to sudden change. (2) Many of the city's populace travel to work by subway or bus. (3) It's all about testing the mood of the populace. (4) Checks and balances required an alert and informed populace.

Is Viri singular or plural?

Viri is the plural of the masculine second declension noun vir, which means "man." Vir is a masculine noun and the "-i" ending is appropriate for the plural nominative of masculine second declension nouns.