Killington Marsh can be accessed in several spots. You can park at the town recreation center (pool, tennis courts, and ball fields) or the Sherburne Library and walk the edges of the fields behind those. A bike path also runs along River Road which can be walked or bicycled.

Further access can be found on the opposite (west) side of the marsh by the River Road Loop Trail (the bike path lane is part of this trail if you wish to walk an actual loop). Drive into Valley Park Road off of River Road, past the apartments, and down a small dirt road that ends at the town water system where there is a small pull-off. Do not park at the apartment complex or block access.

You can follow the River Road Trail into the woods which will go about a mile before ending at Thundering Brook Road. Either return the way you came or walk down Thundering Brook Road to River Road and south to complete the loop (which becomes somewhat long). During migration, it may be more productive to walk the small road back towards the apartments where the shrubby habitat attracts warblers, vireos, and other migrants and residents.

Another spot Killington Marsh can be accessed is along the short boardwalk north of Thundering Brook Road. This is the Thundering Brook Trail and is part of the Appalachian Trail. There is a small parking area on River Road. It ends with a short walk up to a platform at Thundering Brooks Falls which is worthwhile to see while you are there. The boardwalk can be busy particularly during foliage season so if you want to avoid that you can walk along River Road in that area instead if you can find parking near the boardwalk.