Keighley officially joined the Rugby Football Union on Tuesday, 8 April 1879, and the following year, in a match at Bingley, there was a peculiar incident.

The final match of the competition took place at Mytholmroyd on 3 April 1897, and despite a bitterly cold day there was a gate of 2,000 of which over half had travelled from Keighley.

An old newspaper clipping says that "dissatisfaction among the players with regard to terms of payment was the reason for this defeat, and but for this very discreditable piece of business Keighley would have opposed Bradford in the final".

About that time Keighley were one of the leading teams in the Challenge Cup and again in 1907–08 they advanced to the third round by virtue of wins over Brookland Rovers and Whitehaven.

When the game returned to normal there was a hectic period of team rebuilding, and following a really bad season in 1921, six new players were signed from the Furness district.

With such fine forwards as Harold "Hal" Jones and George Dixon[2] from Wigan, and Jimmy Gill from Leeds, already having joined Keighley during their period of revival, there came more important signings in the latter part of the 1930s.

Having beaten Hunslet, Broughton Rangers, Liverpool Stanley in earlier rounds they played Wakefield Trinity in the semi-final.

In November 1938, they were at the top of the Rugby League table, for the first time ever, for a spell of three weeks, but this form was not maintained and they finished 16th with 17 wins, 17 defeats and two draws.

The main reason for the club's decline was that veterans were not replaced quickly enough, and the one promising young player, Reggie Lloyd, was transferred to Castleford in 1938.

They achieved a slender 5–2 advantage in the first leg at Odsal Stadium, and held Keighley to a 5–5 draw in the return encounter at Lawkholme Lane a week later.

And in the 1944–45 season the sides met in the third round of the Challenge Cup when Northern comfortably won on aggregate (35–8) after Keighley had established a 5–0 advantage in the first leg at Lawkholme Lane.

There were also a number of local players who had joined the club during the war years who blossomed into notable members of the senior side.

On 14 February 1948, Keighley were the victims of one of the biggest Challenge Cup upsets when they were defeated 2–10 by Cumbrian junior club, Risehow and Gillhead.

Fortunately for Keighley they had established an 11–0 lead in the first leg of first round at Lawkholme Lane, though they only scraped home on aggregate by a matter of three points.

The Yorkshire Cup defeat seemed to have an adverse effect on Keighley who won only one of their 20 remaining games up to the end of the 1951–52 season and they finished third from the bottom of the league.

The eighth Australian touring side opened their campaign with a game at Lawkholme Lane – for the first time in front of the television cameras.

In the late 1950s, Keighley had some notable backs, in the 1957–58 season fullback Joe Phillips, and three-quarters Dave Smith, Terry Hollindrake, Derek Hallas and Roy Bleasby, between them scored no less than 89 tries.

In October 1985 Keighley were served a winding-up order by Inland Revenue, which was avoided only by selling the cricket field for a reported £30,000 and the training pitch for £65,000.

Peter Roe took over as coach mid-way through the season following the sudden death of Geoff Peggs and the results improved temporarily.

The 1987–88 season saw a recovery on the field, attributed to the signing of experienced players Trevor Skerrett, Gary Moorby and Brenden White.

Attendances increased, averaging 951 in the league and a 2–16 defeat to Widnes in the second round of the Challenge Cup drew a crowd of 4,358 watched Keighley lose 2–16.

Keighley finished in eighth position, winning 15 from 28 games and eventually lost to league leaders Oldham, 24–34 in the end of season play-offs.

[3] Keighley were excluded from the new Super League competition and continue to play in the Second Division, and the disappointment of being denied promotion for a second time due to marketing decisions, cost them fans and sponsors.

Keighley took out an injunction to try to stop the new competition kicking off and only withdrew their legal threat with the offer of more money for lower division clubs and the prospect of promotion and relegation.

[15] In November 2009 a winding up petition against the owners of the club was issued by HM Revenue and Customs (HMRC) for unpaid taxes.

[17] Between the 2010 and 2011 season player coach Barry Eaton left to be replaced by former Super League star Jason Demetriou as player-coach.

[18] 2011 was Demetriou's first season as a coach and the Cougars, having finished second in the league, won promotion to the Championship beating Workington Town 32–12 in the play-off final.

[20] Under March the Cougars played in the Championship until 2014 when they were relegated in controversial circumstances that led the club to consider taking legal action against the RFL.

[33] David Connor, the RFL lead for diversity and equality, praised the club stating: "Rugby League has been breaking down social barriers for more than a hundred years and this is another important milestone.

[35] Club chairman, Mick O'Neill, was awarded the MBE for 'services to Rugby League Football, the community in Keighley, West Yorkshire and to Charity during the Covid-19 Pandemic' in the 2021 New Year Honours.