Lyme disease is the most common vector-borne disease affecting humans in the temperate zones of the Northern Hemisphere. The bacteria responsible belong to the Borrelia burgdorferi sensu lato group and are transmitted by hard ticks of the genus Ixodes, primarily during the nymphal stage. Vector surveillance is therefore essential for assessing risks to the population and disseminating prevention messages. As part of the missions of the National Reference Center (CNR) for Borrelia, the tick surveillance conducted from 2013 to 2016 aimed to study: (1) the density of the Ixodes ricinus vector in Alsace and (2) the tick-borne risk in Alsace for the Borrelia species responsible for Lyme borreliosis. Borrelia miyamotoi, an emerging pathogen, and Anaplasma phagocytophilum, which cause febrile syndromes following tick bites, were also investigated. Four sites with different ecosystems were monitored (rural areas vs. urban or suburban areas; lowland areas vs. mountainous areas). Depending on the sites investigated over the four-year study period, wide variations were observed in nymph densities, ranging from 4 to 143 per 100 m². The density of infected nymphs also varied, ranging from fewer than one infected nymph to more than 8 per 100 m². A mid-mountain site (elevation: 520 m), Murbach, was particularly at risk, but the peri-urban areas around Strasbourg were not without risk either. Alsace therefore remains a region with high tick densities, featuring significant nymph densities and a significantly higher prevalence of human-transmissible pathogens compared to the rest of France.