Neilton is located in northern Grays Harbor County at 47°24′13″N 123°53′14″W(47.403574, -123.887303), within the Olympic National Forest along U.S. Route 101.
The CDP extends north along US 101 to Boulder Creek and south to Cook Creek, while to the east it runs to the 2,654-foot crest of Quinault Ridge. US 101 leads north 4 miles to Amanda Park and south 14 miles to Humptulips. Aberdeen is 39 miles to the south on US 101, and Queets is 29 miles to the northwest.
According to the United States Census Bureau, the Neilton CDP has a total area of 9.7 square miles (25.0 km2), all of it land.
The climate in this area has mild differences between highs and lows, and there is adequate rainfall year-round. According to the Köppen Climate Classification system, Neilton has a marine west coast climate.