Suffolk County Transit operates numerous bus routes in Suffolk County, New York, United States; a few in the town of Huntington are operated by Huntington Area Rapid Transit. The Villages of Patchogue and Port Jefferson, also have had their own local jitney bus routes, although budget cuts have forced these villages to take its buses out of service. Some of them are descendants of streetcar lines (see List of streetcar lines on Long Island). The following tables give details for the routes that primarily service Suffolk County. For details on routes that run into Suffolk County but do not service it primarily, see:

Suffolk County Transit (SCT)

On October 29, 2023, Suffolk Transit introduced the Reimagine Transit Initiative, a full redesign of the bus network. As part of this redesign, there is daily service system-wide with local buses running weekdays until 10 p.m. and to 8 or 9 p.m. on weekends.

All current routes

Most routes west of Port Jefferson and Patchogue are scheduled with 30 minute headways (60 minutes on routes 3, 10 and 15) during weekdays until at least 6:00 p.m. On all routes from Port Jefferson and Patchogue and to the east, including the north-south routes between those two terminals, there are 60-minute headways (except for 30-minute headways on routes 51 and 66). All weekday late evening and weekend service runs on 60-minute headways. Route numbers (not including 110) are lower in the western portion of the county (1 through 17) and higher in the middle and eastern portions (51 through 92). Odd-numbered routes are generally oriented north to south, with even numbers west to east. Timed connections between routes can be made at Long Island Rail Road stations in Amityville, Brentwood, Central Islip, Patchogue, and Riverhead, in Bay Shore and at the Smith Haven Mall. SCT also runs two on-demand systems on the South Fork in Southampton and in East Hampton operated by Hampton Jitney and Via Transportation that replaced the former 10A, 10B, and 10C bus routes. The two on-demand zones connect with Route 92 in Southampton, Sag Harbor, and East Hampton. The zones operate 7 days a week between 6 AM and 8 PM, including holidays. In early June 2024, SCT added a new route, the 56, running between Smithtown Railroad and Kings Park Manor.

History of current routes

These current routes are replacements and reconfigurations of the previous routes that were prefixed with an "S" label, although more localized routes did not have the prefix. The prefix denoted Suffolk County, akin to route labeling in other transit systems around the region. See further down in this article for historical information about all of the former routes. Most of the routes listed in this table replaced all of the former routes on October 29, 2023.

Former routes - S1 to S94

Most of these routes were reconfigured and replaced by the routes listed above on October 29, 2023 in conjunction with the Reimagine Transit Initiative.

Former routes - 1A to 10E

Huntington Area Rapid Transit (HART)

Huntington Area Rapid Transit exclusively serves the Town of Huntington. Service runs weekdays and Saturday until 6 p.m. with no service on Sunday. Service is scheduled approximately every 45 minutes on weekdays and 90 minutes on Saturday.

Former routes

Patchogue Bus

Sometime after January 13, 2016, bus service was discontinued within Village of Patchogue. The routes in the table below ran local within the village on weekdays only.