Sand stringers are subtle, aeolian landforms that reach hundreds to thousands of metres in length and lack a slipface. While hundreds of sand stringers exist beyond the Last Glacial Maximum margin in the Upper Midwest, USA, little is known about the timing and nature of their formation. This research characterizes the morphology and stratigraphy and provides geochronological data from two sand stringers in the upper Mississippi River basin in Minnesota and Wisconsin. The sand stringers investigated have similar west–northwest to east–southeast orientations and are located ~100 km from each other on uplands west and east of the Mississippi River valley. The sand stringer in Goodhue County, Minnesota (GC site) is ~870 m long and 50–80 m wide. To the east, the sand stringer in Eau Claire County, Wisconsin (ECC site) is ~925 m long and 30–50 m wide. The main body of the GC sand stringer is characterized by an ~80–270 cm‐thick silt‐rich surface unit overlying a sandy unit that is underlain by a dark brown paleosol, while the main body of the ECC sand stringer is sandier/coarser, stratified, and overlies outwash. 14C ages, interpreted as minima, at GC indicate formation began prior to 25–20 cal yr BP, while OSL and 14C ages indicate ECC formed ~11.25–8.9 ka. We interpret the main body of GC as equivalent to Peoria Loess, with minor inputs of reworked outwash. We interpret ECC as composed of reworked outwash and local bedrock‐derived sands. Pedogenesis at GC and ECC indicates stabilization with possible minor modification of near‐surface sediments through the Holocene. Differences in stratigraphy and chronology between the two sites highlight the complexity of aeolian systems in the Upper Midwest, interpreted as indicative of the variety of sediment sources contributing to landform development via aeolian processes due to spatial and temporal variability in deglaciation and permafrost melting. Sand stringers are common across the upper Mississippi River basin, USA. Sand stringers were deposited beyond the LGM margin and may be linked to a hypothesized sandy aeolian pulse contemporaneous with permafrost degradation. GC contains an upward coarsening in the main body of the stringer and ECC is predominantly sandy throughout. OSL ages (11.25–8.9 ka) from ECC are similar to regional sandy aeolian depositional ages in prior research. 14C ages from both locations suggest deposition at or post‐LGM.