Rotational spectra of the four main isotopomers of ClClO2 which together span the quantum numbers 10 less than or equal to J less than or equal to 77 and 0 less than or equal to K(a)less than or equal to 34 have been studied in selected regions between 10 and 417 GHz. The in situ syntheses using reactions between FClO2 and either HCl or BCl3 are described. Rotational and centrifugal distortion constants have been derived and used for structure and harmonic force field calculations. The quadrupole coupling constants for both Cl nuclei have been determined and the molecular dipole moment has been derived from low field Stark effect measurements in the submillimeter region. The results are discussed in relationship to published results from a matrix-isolation study, from theoretical calculations, and from studies of related molecules.