It is almost four months since the Castlebar hospital had no confirmed Covid-19 cases. December 10 2020 was the last occasion a zero figure was recorded at MUH.
MUH is among six hospitals in the county to have no confirmed Covid-19 patients as of 8pm last night. The hospital had one suspected case.
Elsewhere in the West, there were nine confirmed cases at Galway University Hospital, five at Portiuncula and two at Sligo University Hospital.
The latest figures show a significant reduction in the number of patients in hospital with Covid-19 across the country.
There were 220 patients with the disease in hospital last night, down 41 on the figure reported earlier, according to the Health Service Executive.
The number of patients with Covid-19 in intensive care units was unchanged at 58.
Around 22 hospitals have nine or fewer Covid-19 patients.