Filming locations
So I've read the posts about the Old Saybrook house and just thought I'd try to give the definite guide from what I know, though by no means complete, and hopefully others can add to figure out just where everything was shot...
One of the things I find fascinating about the movie is how many of the shooting locations in the movie are already well known in CT as interesting attractions in their own right.
Opening shot:
Route 9 northbound to exit 6
The shot starts looking south along Route 9, then pans over to show the exit.
The Old Bishop House:
Old Saybrook location confirmed
So first off the exterior and interior were two different houses.
IMDB has the interior as 34 North Main Street, Essex, Connecticut, USA.
I've never been there, and my understanding is it's a private residence, so good luck getting in, but I'm sure it would have been remodeled since 1971.
Trulia has it listed as being built in 1807.
The exterior is 220 Middlesex Turnpike, Old Saybrook, CT
Here's Old Saybrook's town website map, which shows the zoning. It is zoned for business now, which could explain the lack of habitation or renovations.
http://www.mapgeo.com/oldsaybrookct/?extent=-8057506,5057618,-8057124,5057891&basemap=AP12&thematicmap=ZN
You can also bring up the property records, which has a basic layout of the building.
http://gis.vgsi.com/oldsaybrookct/Parcel.aspx?Pid=4154
Here's a website that calls it "The Old Bishop House" but of course that is from the movie and doesn't seem factual.
http://www.atlasobscura.com/places/old-bishop-house
The house itself is in a pretty bad state. The house is boarded up. There is another house on the same property, with a garage, and that house has all windows and doors removed
If you are planning on going, be aware this is private property, and there are "No trespassing signs" very visible, so there is the danger of prosecution. And, the property is highly overgrown (though the driveway is easily passable), and during the summer there is loads of poison ivy growing around the property.
It is very easy to recreate the shot of Jessica running down the driveway away from the house, BTW. But again, you would be trespassing.
The ferry to the "island":
Chester & Hadlyme, CT, location confirmed
The ferry is the Chester/Hadlyme ferry across the Connecticut River. Still in operation, and in Hadlyme brings you to Gillette's Castle, a very interesting place to visit.
http://en.wikipedia.org/wiki/Chester%E2%80%93Hadlyme_Ferry
http://en.wikipedia.org/wiki/Gillette_Castle_State_Park
The "town":
Chester, CT, one location confirmed
The shot of them entering the town is the intersection of Maple and Main Streets, in Chester, CT.
You can see the same building on the corner, updated obviously, and the circular intersection.
https://www.google.com/maps/@41.402375,-72.44953,3a,75y,126.57h,72.1t/data=!3m4!1e1!3m2!1szKLxVSSLAqgNFhRFCV5N8g!2e0
Swimming area:
Pattaconk Reservoir, Chester, CT, confirmed
TheXmanCometh nailed this one. Great job.
Here's the thread:
http://www.imdb.com/title/tt0067341/board/thread/237004106
The orchid:
location unknown
The orchid, after 40 years, may or may not still exist. I would think it's still around as apple orchids in this area are still profitable, but it could be gone after all this time.
The graveyard:
Venture Smith Grave at First Church, East Haddam, confirmed
The story of Venture Smith is true, and his gravestone resides at the First Church of Christ cemetery in East Haddam.
According to other sources most if not all of the graveyard scenes have been filmed there. There are some discrepancies though, such as, the white fencing in the movie has been removed and replaced with a stone wall.
I'm planning on future visit to try to match shot for shot the gravestones in the movie.
The Black Whale Antiques
location unknown
So this one is interesting; there IS a Black Whale antique shop in Hadlyme, CT, but it's only been in operation since 1982. So is there any connection to the one shown in the movie, which looks like it operated out of a barn? A future road trip and a talk with the owners will hopefully shed some info.
http://www.blackwhaleantiques.com/
The dam:
Johnsonville Millpond dam, East Haddam, CT, confirmed
Johnsonville is another interesting place, with a storied history and many fascinating tales. Presently it is up for auction, though I don't think the mill pond dam is in any danger of being removed.
Here are some links which explain it's history much better than I would:
http://www.damnedct.com/johnsonville-east-haddam
http://johnsonville.omeka.net/
If you visit, Johnsonville Road is a public road, so it is easy enough to drive past, and if you can find a good place to part, you can also walk down the road. But I would caution venturing too far onto the grounds, as it is a highly watched area, with numerous "No Trespassing" signs and even cameras, and possible security presence discouraging trespassers.
Machimoodus State Park borders on the property and has very good views of all the buildings.
Recently (October 2014), Johnsonville was put up for auction and purchased by an unknown corporation The fate of the village at this time is unknown.