When Was The First Day Of Summer 2024. The first day of summer this year is thursday, june 20, 2024, per the almanac. Today (june 20) the summer solstice — the longest day of the year in the northern hemisphere — will begin, and it will be the earliest solstice in 228 years.
Thursday, june 20 is the official first day of northern astronomical summer for 2024 — summer solstice — which is the longest day of the year for this half of the planet. That also happens to be the summer solstice, aka the start of summer.