Geochemical and isotopic compositions were determined in stream sediment and parent rocks collected in April 2017 and June 2017 and in nearshore sediment collected bimonthly in sediment traps from May 2017 to June 2018 in the coastal zone and 12 drainages of southwest Puerto Rico: Rio Loco, Yauco, Guayanilla, Macana, Tallaboa, Matilde, Portugues, Bucana, Inabon, Jacaquas, Descalabrado, and Coamo. Geochemical compositional data include: a) total contents of major, minor, trace, and rare earth elements in the <0.063 mm-diameter fraction of terrestrial (n=53) and nearshore sediment (n=63) and powdered rocks (n=19) analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectroscopy (ICP-MS); b) major oxide contents of stream sediment (n=46) and rocks (n=19) determined by wavelength dispersive x-ray fluorescence spectrometry (WD-XRF); and c) total organic carbon and carbonate contents of stream (n=48) and nearshore (n=64) sediment determined coulometrically. Isotopic compositional data include: 1) strontium isotope ratios (87Sr/86Sr) determined by thermal ionization mass spectrometry in the <0.063 mm-diameter fraction of select stream (n=50) and nearshore (n=40) sediment, and in all rocks; and 2) activities of the short-lived cosmogenic nuclides beryllium-7, cesium-137, and excess (unsupported) lead-210 determined by gamma spectrometry on bulk nearshore sediment (n=44). The percentage by weight of the <0.063 mm-diameter sediment fraction (percent fines), the median grain size, and the silt to clay ratio are reported for stream (n=48) and nearshore (n=64) sediments. These data accompany Takesue, R.K., Sherman, C., Ramirez, N.I., Reyes, A.O., Cheriton, O.M., Rios, R.V., and Storlazzi, C.D., 2021, Land-based sediment sources and transport to southwest Puerto Rico coral reefs after Hurricane Maria, May 2017 to June 2018: Estuarine, Coastal and Shelf Science, v. 59, p. 107476, https://doi.org/10.1016/j.ecss.2021.107476.