Moist to wet forests and thickets, wet open depressions, vernal pools, and wet fields and ditches.

This is rather similar to the less common Carex typhina. In addition to the features noted in the key, several characters are helpful in the field. In C. squarrosa, perigynium beaks radiate in all directions at maturity, i.e., the lowermost perigynia have beaks that point downward, perigynia in the middle of the spike have beaks that point outward, and perigynia at the apex have their beaks pointing upward. In C.typhina, even the lowest perigynium beaks point ± outward. Though there is some overlap, the leaves of C. squarrosa are distinctly narrower than those of C. typhina, the widest leaves of C. squarrosa are 3.1-5.7 mm broad while those of C. typhina are 5.3-7.5 mm.

Long known from southeastern Michigan (Lenawee, Monroe, Washtenaw, and Wayne Cos.), where collected as early as 1832. Occurrences remained few and confined to this area until the late 1990's when scattered sites began to be discovered, north to Gratiot and St. Clair and west to Berrien Cos., so apparently the species is increasing and spreading northward.