There are plenty at CheongCho Lake in Sokcho, as well. The cormorants, standing on provided perches and drying their thin wings are the most interesting here. For size and grandeur, I can't think of any better than the cranes in Cheolwon, but there aren't many specific details in the brief article.
Elsewhere online, I first found one should look for unplowed fields - the plowed fields will also have cranes, but the unplowed fields will have happier cranes.
The Visit Korea site has more information:
The most spectacular views are generally at sunrise, between noon and 2pm, and at sunset, and for the rest of daylight hours you can choose from a wide variety of attractions located near the demarcation line. North Korean infiltrating the second tunnel, Woljeong Station Observation Deck, the former Labour Party building, Baekmagoji highland (백마고지) and Dopiansa Temple (도피안사) all reside nearby. Since the Cheorwon Plain is located north of the Civilian Control Line and normally not opened to civilian access, the ecosystem is very well preserved.
Tour Course Information
* The Four Best Bird-watching Spots
1) Togyo Reservoir (Yangji-ri): Birds dancing/taking off en masse before sunrise, vultures.
2) Dongsong Reservoir (Gangsan-ri) area: White-naped cranes, hooded cranes, wild geese.
3) Woljeong Station Observation Deck area: Observing DMZ, bird watching.
4) Saemtong area (habitat of migratory birds): Migratory birds including cranes.
* Caution: Illegal hunting is prohibited by any means, whether it is by means of traps, snares, toxic substances, air rifles, or shotguns.
November ~ February
Private cars cannot cross the CCL (Civilian Control Line) but buses are available and frequent (so the page claims). The site also has specific directions for travelers from many starting points.
Turumi.go.kr is the local site.
I went to Cheolwon perhaps eight years ago with the Royal Asiatic Society. I think I need to return soon. Perhaps next weekend.
Really off-topic - The Turumi site is good but has interesting English, most notably "Introduce of cranes" and "Introduce of crames" next to one-another. Bizarro-Brian posted about another site with similar problems and a commenter defended English speaking staff and pointed the blame elsewhere: Mr Foreman said, "...I can say (at least in my experience) that the problem often resides with the company doing the actual coding of the site. Often (and regrettably) text cannot simply be cut and paste into the application that is being used to build the site. So, people who often have no knowledge of English whatsoever are asked to physically type certain portions of the site into various different applications and that is, obviously, never given back the the "conscientious native speaker" to proofread; that is where the problems resides."
The problem then seems to reside with incompatible software.