Cells regulate adhesion to the fibrillar extracellular matrix (ECM) of which fibronectin is an essential component. However, most studies characterize cell adhesion to globular fibronectin substrates at time scales long after cells polarize and migrate. To overcome this limitation, a simple and scalable method to engineer biomimetic 3D fibrillar fibronectin matrices is introduced and how they are sensed by fibroblasts from the onset of attachment is characterized. Compared to globular fibronectin substrates, fibroblasts accelerate adhesion initiation and strengthening within seconds to fibrillar fibronectin matrices via α5β1 integrin and syndecan‐4. This regulation, which additionally accelerates on stiffened fibrillar matrices, involves actin polymerization, actomyosin contraction, and the cytoplasmic proteins paxillin, focal adhesion kinase, and phosphoinositide 3‐kinase. Furthermore, this immediate sensing and adhesion of fibroblast to fibrillar fibronectin guides migration speed, persistency, and proliferation range from hours to weeks. The findings highlight that fibrillar fibronectin matrices, compared to widely‐used globular fibronectin, trigger short‐ and long‐term cell decisions very differently and urge the use of such matrices to better understand in vivo interactions of cells and ECMs. The engineered fibronectin matrices, which can be printed onto non‐biological surfaces without loss of function, open avenues for various cell biological, tissue engineering and medical applications. Biomimetic fibrillar fibronectin matrices are engineered using 3D‐printed microgrids and simple solution shearing. Attaching to fibrillar fibronectin matrices, fibroblasts strengthen adhesion initiation within seconds and enhance long‐term migration and proliferation by employing β1 integrin and syndecan‐4. This rapid and continual fibrillar mechanosensing explains how fibrillar extracellular matrices modulate cell decisions in native tissues.