In ONE formula unit of CaF_2, how many individual ions are there?

In one formula unit of $C a {F}_{2}$, there are 3 ions, one cation, and 2 anions.
$C a {F}_{2}$ is the result of ionic bonds between $C {a}^{2 +}$ and $2 \times {F}^{-}$. Electrical neutrality demands this stoichiometry. The resultant fluorite structure is exceptionally strong.