Periodical cicadas have very long life cycles and depending upon what part of the country you are in will dictate which Brood will be emerging this year. This year is a Brood II year which is primary on the north eastern seaboard and inland a bit. If you live in an area outside of this and see some periodical cicadas they likely are not from Brood II but rather some early risers or some stragglers from your regional brood. Animals don’t read books so they don’t always know which year they’re “supposed” to emerge. There are always some outliers.
Here’s a link to a LINK for where you can check to see when you can expect the Periodical Cicadas to emerge in your area. Missing out this year? Maybe next year will be better!