The hosts, whose past two games had been postponed, went in front when Tony Watt converted Nathan McGinley’s cross.
Mark O’Hara tucked away a penalty after Watt was fouled by Iain Vigurs.
And, after the visitors had their second effort cleared off the line, Callum Lang and Devante Cole added further Well goals.
Stuart Kettlewell’s Ross County have not won in the league since mid-September.
Motherwell last played on 27 September, with their games against Kilmarnock and St Mirren called off over those clubs’ Covid-19 issues.
And the Steelmen have had their own coronavirus problems with one positive test confirmed on Friday.
There was a further headache for Stephen Robinson midway through the first half when goalkeeper Trevor Carson raced out his box to make a headed clearance and appeared to land awkwardly. Aaron Chapman was sent on for his debut.
There had been few chances to speak of up until that point but McGinley’s run and cross changed all that with Watt getting in front of Alex Iacovitti to fashion a shot past Ross Doohan.
Regan Charles-Cook had earlier tested Carson with a tame header and though the midfielder was able to beat Chapman, Declan Gallagher was well placed to clear off the line in first-half stoppage time.
Robinson’s side started the second half with intent and Watt cantered into the box only to be felled by former Motherwell man Vigurs, who was booked. O’Hara confidently beat Doohan.
Watt then cleared a Ross Stewart headed off the line and Stewart’s frustration continued with his next two efforts both off target.
Lang was introduced in place of Christopher Long and quickly ended the match as a contest, turning Gallagher’s header at a corner over the line from close range.
And Chapman’s long ball was nodded on by Watt for Cole to finish high into the net – his first goal since returning to the club from Doncaster Rovers.
Man of the match – Tony Watt
What did we learn?
After such a long gap since their last match, Motherwell initially lacked sharpness but settled after Watt’s opener.
The energy and pace of their attacks in the second half in particular caused problems for Ross County.
Kettlewell’s side did not start the match looking like a team that would lose 4-0 but defensive slackness and poor finishing was their undoing at Fir Park.
The Staggies had a decent start to the season but Motherwell’s ascent up the table is a reminder of how quickly league placings can change in the Premiership.
What did they say?
Motherwell manager Stephen Robinson: “To put on a level of performance like that and (midfielder) Mark O’Hara playing at centre-half was outstanding. Tony Watt was unplayable. If he keeps those fitness levels, energy and desire then we’ve got a really good centre-forward.
“Devante Cole for someone who hasn’t played for such a long time was very good. Overall, really, really pleased with the performance.”
Ross County manager Stuart Kettlewell: “There was just a real degree of naivety in the second half. It’s a real frustration for me. When we go behind, there seems to be a real softness in us.
“We had numerous chances ourselves. Ross Stewart’s had three that I would expect him to finish.”