To reconstruct the tectono-sedimentary histroy of the fore-arc basin that developed along the Cretaceous–Paleogene arc-trench system in Japan, a provenance analysis is carried out by U–Pb dating detrital zircons, particularly for Cretaceous–Paleogene sandstones/conglomerates sporadically found in five distinct areas of the Kanto and southern Tohoku district, i.e., the Shoya Formation in Saku, the Kanohara Conglomerate in Shimonita, the Yorii Formation in Yorii (Kanto Mountains), the Nakaminato Group and Oarai Formation (northern Kanto), and the Futaba Group (southern Tohoku), for which geotectonic identities have been ambiguous. U–Pb dating of detrital zircons from 14 sandstone samples constrains their depositional ages to the Late Cretaceous and early Paleocene, and also their provenance. These results reveal the following new facts. 1) The Shoya Fm and Nakaminato Gr are of the Maastrichtian age; the Kanohara Conglomerate, Yorii Fm, and Oarai Fm are of the Paleocene (mostly Danian and up to Thanetian); and, the top of the Futaba Gr reaches up to the Campanian. 2) In addition to previously known partial similarities in lithofacies and fossils, newly obtained U–Pb age spectra of detrital zircons confirm that all these units represent the eastern extension of the Izumi Group in Shikoku and Kii Peninsula, and they share the same provenance dominated by late Cretaceous granitoids. 3) These new age data indicate that the spatial dimensions of the Cretaceous–Paleogene Izumi fore-arc basin extended over 1,300 km from western Kyushu to southern Tohoku along the arc, whereas its width may have reached 100 km across the arc. 4) The Median Tectonic Line (MTL) in Kanto is represented by a low-angle fault, which separates Ryoke-derived strata of the Izumi affinity from structurally underlying high-P/T Sanbagawa metamorphic rocks. 5) The MTL runs along the northern margin of the Kanto Mountains and extends further to the east, probably even into NE Japan, off-shore from northern Kanto and southern Tohoku district.