Mountrath (Irish: Maighean Rátha, meaning 'homestead of the ringfort') is a town in County Laois, Ireland. The town lies on the R445 midway between Dublin and Limerick, exactly 96.5 km (60 mi) from both cities. The town was bypassed by the M7 motorway in 2010, leading to a significant easing of traffic congestion in the town.

As of the 2022 census, Mountrath had a population of 2,070. The river that flows through the town is called the Whitehorse and gets its name from the white colouring that was present in its water from the whiskey distillery that used to be in the centre of the town.

The important Synod of Ráth Breasail was held near Mountrath in 1111.

In the beginning of the 17th century, the lands around Mountrath became the property of Charles Coote. Despite the wild surrounding country, which was covered with woodlands, he laid the foundation of the present town. In 1628, Coote obtained for the inhabitants a grant of two weekly markets and two fairs and established a very extensive linen and fustian manufactory. In the year 1641, as a Royalist supporter, much of his property was destroyed during the Irish Confederacy in the War of the Three Kingdoms.

His son, Sam Coote, regained the castle and estate of Mountrath, along with other properties and following the Restoration, was created Earl of Mountrath. This title was extant until the death of Charles Henry, the 7th Earl, in 1802, when it became extinct. Newpark, adjoining the town, was the residence of the Earl of Mountrath. In 1831, the town contained 429 houses; iron was made and wrought here till the neighbouring woods were consumed for charcoal fuel. The Post Chaise Companion, published in 1805, states that:

"Near Mountrath is an extensive bank containing, or rather, formed of excellent iron ore, within a few metres of the surface; here an iron and metal foundry has been established and wrought some years since with great success; but at present, from the scarcity of charcoal, on the destruction of the neighbouring woods, the furnaces are seldom employed; it is much to be regretted that such a valuable manufacture should be discontinued on the above account, as the country abounds with bogs, and charred turf might probably be substituted in the place of charcoal for most purposes."

In his 1837 Topographical Dictionary of Ireland entry for Mountrath, Samuel Lewis states that:

"an extensive factory for spinning and weaving cotton is carried on by Mr. Greenham, who employs 150 persons in the spinning mills, and about 500 in weaving calicoes at their own houses; the average quantity manufactured is from 200 to 250 pieces weekly. Stuff-weaving is also carried on extensively; there is a large brewery and malting establishment, and an extensive oil mill; and the inhabitants carry on a very extensive country trade."