Kilmarnock (/kɪlˈmɑːrnək/ kil-MAR-nək; Scots: Kilmaurnock; Scottish Gaelic: Cill Mheàrnaig, IPA: [kʲʰiːʎ ˈvaːɾnəkʲ]), meaning "the church of Mernóc", also colloquially referred to as Killie, is a town and former burgh in East Ayrshire situated in southwest Scotland. The town has served as the administrative centre of East Ayrshire Council since 1996 and is the region's main commercial and industrial centre. The town has a total of 284 listed buildings and structures as designed by Historic Environment Scotland, including the Dick Institute, Dean Castle, Loanhead School and the original 1898 building of Kilmarnock Academy, with post-war developments of the controversial 1970s regeneration such as The Foregate and Clydesdale Bank building being considered for listed building status.

The first passenger conveying railway in Scotland originated in Kilmarnock in 1812 as a horse-drawn four-foot-gauge (1.2 m) plateway and became known as the Kilmarnock and Troon Railway. The first printed collection of works by Scottish poet Robert Burns was published in 1786 in Kilmarnock. Poems, Chiefly in the Scottish Dialect, was published by John Wilson, and became known as the Kilmarnock Edition. The internationally best-selling whisky Johnnie Walker was established in the town in the 19th century and was produced and bottled at the Hill Street plant until closure in 2012, following an announcement by owners Diageo in 2009 that the plant would close as part of company restructuring.

The town grew considerably during the 1870s and the town's growth subsumed the village of Bonnyton, and by the 1960s, new purpose built suburbs such as New Farm Loch were constructed to accommodate the increasing population of Kilmarnock. By mid-2020, the population of the town was estimated to be 46,970, making Kilmarnock the 14th most populated settlement in Scotland as well as the largest town in Ayrshire by population.

The name Kilmarnock comes from the Gaelic cill (cell), and the name of Saint Marnock or Mernoc who is also remembered in the name of Portmarnock in Ireland and Inchmarnock. It may come from the three Gaelic elements mo, 'my', Ernán (name of the saint) and the diminutive ag, giving Church of My Little Ernán. According to tradition, the saint founded a church there in the 7th century. The name Kilmarnock literally means "Marnock's Church". There are 12 Church of Scotland congregations in the town, plus other denominations. In 2005, the Reverend David W. Lacy, minister of the town's Henderson Church, was elected Moderator of the General Assembly of the Church of Scotland.

The town's precise origins are largely unclear, however, it is believed that a community was established between the fifth–seventh centuries at the Laigh Kirk Church by a Saint Marnock. The earliest known mention of the town was in the 14th century, with Clan Boyd coming to prominence in the area during that time, building the Keep of the Dean Castle. The Romans held a "tentative grip" on the area in and around Kilmarnock, with forts nearby at Loudoun Castle as well as possessing costal harbours around Ayrshire. Early references to the town are vague in regards to population numbers and the geographical size of the town, however, it is widely believed that at this time, the town was little more than a small cluster of dwellings situated around the Laigh Kirk church.

By the end of the sixteenth century, Kilmarnock had become a burgh of barony, and had a weekly market stall and by the 1600s had grown into a small network of narrow streets, with the population relying on industries such as spinning wool, knitting bonnets and the manufacturing of metal cutlery to make a living. A fire engulfed the town in 1668, following the hunting of Covenanters by government troops.

The core of the early town appears to have lain around what is now the Laigh Kirk, Kilmarnock (Low Church), although the oldest parts of the current building are no earlier than the 17th century, extending north and northwest. In 1668 the town was largely destroyed by an accidental fire. About 120 families lost most of their possessions and were forced to live destitute in the fields surrounding the town. These tradespeople had no other way of making a living and had already been driven to the edge of poverty by having troops stationed with them as part of the anti-Covenanter measures. Parish churches throughout Scotland collected money for the relief of these homeless citizens.

In 1592, King James VI of Scotland granted a charter to Thomas, Lord Boyd, erecting Kilmarnock into a burgh of barony. The charter confirms that the Boyd family to be in possession of the land of Kilmarnock and assures any future line of succession. At the beginning of the 16th century, Kilmarnock was described as "a large village and of great repair" with nearby Kilmaurs notably larger than Kilmarnock. However, over the course of the next one hundred years, the expansion of Kilmarnock was evident. Its expansion led to Kilmarnock becoming larger than Kilmaurs and becoming Ayrshire's largest inland centre and challenging the supremacy of the royal burghs of Ayr and Irvine. During the 19th century, due to the growing rate of expansion due to the industrial expansion, Kilmarnock's population growth increased significantly from 6,000 in 1800, 21,000 in 1851 and 35,000 by 1901.