Kirkby-in-Ashfield is a market town in the Ashfield District of Nottinghamshire, England. With a population of 25,265 (according to the 2001 National Census), it is a part of the wider Mansfield Urban Area. The Head Offices of Ashfield District Council are located on Urban Road in the town centre.

Kirkby-in-Ashfield lies on the eastern edge of the Erewash Valley which separates Nottinghamshire and Derbyshire. Kirkby, as it is locally known, was originally a Danish settlement (Kirk-by translates as 'Church Town' in Danish) and is a collection of small villages including Old Kirkby, The Folly (East Kirkby), Nuncargate and Kirkby Woodhouse. It is mentioned in the Domesday Book and has two main churches: St Wilfrid's, a Norman church, which was gutted by fire on 6 January 1907 but quickly re-built; and St Thomas', built in the early 1910s in neo-gothic style.

Kirkby Castle is said to have dated back to at least the 13th Century. Its owner in 1284 Robert de Stuteville was fined by King Edward I for not attending the Royal summons. However, in 1292 Robert clearly forgiven, hosted the king at the Castle to a nights stay.

On the edge of Kirkby near Annesley is Portland Park (known to local people as "the quarries") a mixture of woodland and grassland areas which, together with a number of small ponds and streams, are home to a wide variety of wildlife. The visitor centre, which doubles up as local cafe The Wild Rabbit, was opened in October 1994, and is an environmentally friendly building and a centre of excellence for energy conservation. The building is also used as a popular venue for local live acts and other entertainment. The area surrounding The Wild Rabbit Cafe is a place of scientific interest due to the unique limestone outside to the rear of the cafe.