In the town of Mizuho there's several Clannad locations including the school hill. So I took the train to the closest train station which is Hakonegasaki Station to check it out.
Image from Episode 1 - 00m29s
My image is slightly closer up, but you can see the railings that match.
Image from Episode 1 - 00m30s
You can see the bottom of these stairs in the anime picture.
Image from Episode 1 - 00m40s
Not a match picture, but it was the end of the sakura season so I thought I'd include this since it looked so nice.
Image from Episode 1 - 01m51s
Tomoya and Nagisa is standing a bit further down the hill in the anime shot, but you can see the railing and the curved path that matches.
Image from Episode 9 - 19m56s
This is at the top of the hill. Unfortunately the school itself doesn't match. The school shown in the anime is located somewhere else.
Japanese Clannad volume 1 DVD cover
A similar shot was also used for the cover of the first DVD volume of the anime in Japan.
Closeup of one of the sakura flowers. The hill would probably have been even more beautiful earlier in the blooming season, but at least there were still some sakura left when I visited this location. ^_^
Image from After Story Episode 4 - 19m31s
At the very bottom of the hill there's also these stairs.
Image from After Story Episode 8 - 10m30s
The stairs lead up to this park area which was also shown in the anime.
Image from After Story Episode 8 - 10m58s
You can see this monument to the right in the anime shot.
Image from Episode 1 - 03m19s
This road to the right of both the hill and the stairs to the park is shown in the Clannad OP.
Image from After Story Episode 4 - 19m16s
It is also shown a few other times in both the original series and After Story.
This location was visited on 2014/04/13.
Mizuho official website
Special thanks to the ones who went here before: