The Northern Sound region has seen 180 new Covid-19 cases in the week up to Friday.
Monaghan now has the second highest 14-day incidence rate in the country after Donegal, at 188.9 per 100,000.
Its rate is now well above the level where further restrictions were put in place in Donegal and Dublin.
The county has seen 116 cases confirmed in the week to Friday.
Cavan has also seen an increase over the past week but at a slower rate than Monaghan.
64 cases have been recorded in Cavan, giving an incidence rate of 84 per 100,000 - the 10th highest in the country.