Haemaphysalis longicornis (Asian Longhorned Tick [ALT]) was first recognized in the US, outside of customs, in New Jersey in 2017, and now has been documented in 2 Delaware counties. In Asia, where this species is native, and other parts of the world, the ALT is a known or suspected vector of various pathogens to humans, wildlife, and livestock. The ALT's role as a pest of medical and veterinary concern highlights its potential to become an economic burden in the US. The detection of ALT in the eastern US has prompted an initiative to identify and monitor its establishment and spread. Delaware is now the twelfth US state where ALT has been documented. The continued monitoring of this species is of great importance to the agricultural and public health communities.