Most often through the cove joint where the floor meets the wall, then through wall cracks, block cores, stone-mortar joints, and porous concrete, all driven by hydrostatic pressure from water-saturated clay soil. Window wells, floor drains, and sewer backups are other paths.
More detail
The dominant entry path in Cincinnati is the cove joint, the seam where the basement floor slab meets the foundation wall. It is a deliberate construction gap, and when the soil outside is saturated and under hydrostatic pressure, water is pushed up and in at that seam, which is why so many wet basements show water tracking along the base of the wall. Beyond the cove joint, water enters through vertical and diagonal cracks in poured walls, through the hollow cores and mortar joints of block walls, through the mortar joints of pre-1940 stone foundations, and by slow diffusion through porous concrete itself. The shared driver is hydrostatic pressure from Cincinnati's water-holding clay soil after heavy or prolonged rain. Other distinct entry paths we diagnose: window wells that fill with water and overflow the window into the basement (common with finished basement bedrooms and a frequent egress-window job); below-grade walkout doors, stairwells, and bulkheads where surface water pools and finds the threshold; floor drains and the cove joint near a sump that is undersized or failed; and, in the older combined-sewer neighborhoods, sewer backups that push water up through the floor drain during heavy rain, which is a different problem from groundwater seepage and is addressed through MSDGC backwater-valve programs rather than waterproofing. The on-site assessment maps which paths are active for your home, because the right solution depends entirely on whether you are fighting hydrostatic groundwater (drainage), a single crack (injection), surface water at an opening (grading and well drainage), or a sewer surcharge (backwater valve).