From what I understand of it from a brief Google search. Counter-pastoral was a term coined by Raymond Williams in his cultural analysis: The Country and the City. Its name is potentially a bit misleading as it is not, as one might be initially led to believe, a reaction against pastoral poetry (pastoral poetry basically portrays rural life, particularly in an idealised manner), but rather: "[T]hey are instances of a self-consciousness about how pastoral has failed and will fail to account for the pain of rural life . . . at the same time as they are little attempts to reevaluate the words against that failure and actually express and overcome the latter."
From pastoral poetry emerged "the notion of rural life as simple, natural, and unadulterated, [which] le[ft] an image of the country as a Golden age. This is, according to Williams, “a myth functioning as a memory” that dissimulates class conflict, enmity, and animosity present in the country since the 16th century."
In other words: whereas pastoral poetry idealised rural life, counter-pastoral poetry attempted to depict the reality of pastoral life. Both the good and the bad.