Just to close the loop:
For the project in question, we ended up going with cJSON. We chose this one from the list of C libraries linked from json.org. Per the homepage, cJSON is:
An ultra-lightweight, portable, single-file, simple-as-can-be ANSI-C compliant JSON parser, under MIT license.
This happened to be a good fit for the particular project at hand, and the library worked out fine.