Accepted answer is a good and correct answer — but no references! Comprehensive rules. Emphasis mine.
305.1. A player who has priority may play a land card from his or her hand during a main phase of his or her turn when the stack is empty. Playing a land is a special action; it doesn't use the stack (see rule 115). Rather, the player simply puts the land onto the battlefield. Since the land doesn't go on the stack, it is never a spell, and players can't respond to it with instants or activated abilities.
Since you can't respond to it, you can't counterspell it.
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305.9. If an object is both a land and another card type, it can be played only as a land. It can't be cast as a spell.
Even if you added another card type to the land somehow, you cannot cast it as a spell.
There are those who don't like to slog through the comprehensive rules, that's understandable, but Wizards was pretty clear in the Basic Rulebook on this point too:
Although lands are permanents, they aren’t cast as spells. To play a land, just put it onto the battlefield. This happens immediately, so no player can do anything else in response. You can play a land only during one of your main phases while the stack is empty. You can’t play more than one land a turn.