- Southern Terminus:
- Montauk Highway (NY 27A) in Islip
- Northern Terminus:
- Main Street (NY 25/NY 25A), Middle Country Road (NY 25), and North Country Road (NY 25A) in Smithtown
- 9.42 miles
NY 111 is a major north/south route in central Suffolk. It begins at Montauk Highway (NY 27A) in Islip and runs north with interchanges at Sunrise Highway (NY 27) and the Southern Parkway. When NY 111 crosses Suffolk Avenue (CR 100), it changes names to become Joshua's Path. Just south of the Long Island Expressway (I-495), Joshua's Path merges into Wheeler Road (CR 17). CR 17 ends and Wheeler Road takes on the NY 111 designation. Just north of Veterans Highway (NY 454), Wheeler Road merges into Townline Road (CR 76). One block to the east, NY 111 splits off from CR 76 as Hauppauge Road. It continues north to the point where Main Street (NY 25/NY 25A) splits into Middle Country Road (NY 25) and North Country Road (NY 25A) and ends there.