For me — no matter how they define summer in the United States and elsewhere — summer starts on 1 June and ends on 31 August. Therefore, today is the last day of summer.
This also is the title of the first collection of photographs by Jock Sturges, published in 1991. These beautiful black and white photos were shot mostly in Northern California and Montalivet, France, between 1978 and 1990. Finally, the two photos there are also entitled Last Day of Summer #1 and Last Day of Summer #2. The excerpts from the afterword by Sturges explain the title.