We study the (generalized Dolbeault) cohomology of generalized complex manifolds in 4 real dimensions. We show that in 4 real dimensions, the first cohomology around a nondegenerate type change point is given by holomorphic (1,0) forms defined on the type change locus. We use this to compute the cohomology of a neighbourhood of a compact component of the type change locus as well as that of the blow-up of a type change point. Finally, we use these computations to determine the generalized cohomology of some concrete examples.