Here we present median grain size (micrometer) and mud content (%) data of the entire intertidal Dutch Wadden Sea that was sampled every year between 2009 and 2019. As can be read in the accompanying paper, the raw data were taken on a 500 m grid and on randomly located stations. Between 4,051 and 4,246 samples were collected and analyzed every year, which made a total of 45,808 over the study period. Most of the sampling took place in the months between June and August and the stations were not sampled at the same dates across years. Sampling stations were visited by foot during low tide and by boat during high tide. Sediment samples were taken with a small core with a diameter of 33 mm from the surface of the intertidal flats to a depth of 4 cm and then frozen at -20 degrees C. In the laboratory, the samples were freeze-dried for up to 96 h and then homogenized with a mortar and pestle. Homogenized samples were weighed and placed into 13 ml polypropylene auto-sampler tubes with degassed water that was purified by means of reverse osmosis. Grain size distributions were measured with a particle size analyzer which uses laser diffraction and Polarization Intensity Differential Scattering technology (Coulter LS 13 320, optical module 'grey'). It measures grain sizes from 0.04 to 2000 micrometer in 126 size classes. It is important to note that our samples were not treated with hydrogen chloride and hydrogen peroxide to remove calcium and organic material. For further details concerning sediment analysis we refer to the accompanying paper.