You are correct. 17 year broods emerged in 2019, 2020, 2021, and now 2024. There are different broods of cicadas, 12 on a 17 year emergence cycle and 4 on a 13 year emergence cycle. For 12 of every 17 years, there will be a 17 year cicada brood emergence. The broods arriving this year both emerged at the same time in 1803. The 17 year brood, Brood XIII, is the Northern Illinois Brood (brown on the map linked below). The other is the Great Southern Brood (Brood XIX) shown in blue. Brood XIX is the geographically largest group. It also just happens to nearly coincide with the eclipse, and the eclipse path goes right through the area of emergence.
You are correct. 17 year broods emerged in 2019, 2020, 2021, and now 2024. There are different broods of cicadas, 12 on a 17 year emergence cycle and 4 on a 13 year emergence cycle. For 12 of every 17 years, there will be a 17 year cicada brood emergence. The broods arriving this year both emerged at the same time in 1803. The 17 year brood, Brood XIII, is the Northern Illinois Brood (brown on the map linked below). The other is the Great Southern Brood (Brood XIX) shown in blue. Brood XIX is the geographically largest group. It also just happens to nearly coincide with the eclipse, and the eclipse path goes right through the area of emergence.
https://en.m.wikipedia.org/wiki/File:Periodical_Cicada_Broods_of_the_United_States.png