This dataset contains measured and processed data for a static reflective D-band metasurface / RIS prototype developed by the University of Oulu within the TERRAMETA project. The dataset supports the experimental validation of a simplified design methodology for highly efficient anomalous reflective metasurfaces with wide steering angles at 140 GHz. The associated work demonstrates measured reflection efficiencies above 82%, reaching at least 84% for steering angles up to 68°, with good agreement between simulation and measurement. The metasurface is implemented on a 100 µm-thick Megtron-7 substrate with relative permittivity εr = 3.2 and loss tangent tanδ = 0.002, backed by a continuous metallic ground plane. Each unit cell has dimensions 0.28 mm × 1.01 mm and consists of a rectangular metallic patch whose length is varied to tune the reflection phase across approximately 360°. Periodic super unit cells (SUCs) are designed according to the generalized reflection law to enable anomalous beam steering. Depending on the target reflection angle, each SUC comprises between 8 and 16 unit cells. The fabricated prototypes cover steering angles of 28°, 48°, and 68°, with overall metasurface sizes of approximately 36.48 mm × 21.4 mm, 34.56 mm × 21.4 mm, and 27.36 mm × 21.4 mm, respectively. The dataset includes: raw measured data in MATLAB .mat format, processed data in .xlsx format (including both measured and simulated results), a MATLAB script, plot_code.m, to reproduce representative plots from the dataset. This dataset is intended to support reproducibility, secondary analysis, and reuse in research on THz / D-band RIS, anomalous reflection, and 6G reconfigurable intelligent surfaces. This dataset accompanies the publication: D. Kong, T. D. Phan, J. Palosaari, J. Juuti, A. Pärssinen, and P. J. Soh, “A Simplified Method for Designing Highly Efficient Reflective Metasurfaces With Wide Steering Angles,” IEEE Antennas and Wireless Propagation Letters, vol. 23, no. 11, pp. 3664–3668, Nov. 2024. doi: 10.1109/LAWP.2024.3439328.