Idaho's 21st legislative district is one of 35 districts of the Idaho Legislature. It is currently represented by Regina Bayer (Republican), Steven Harris, (Republican), and Megan Kiska (Republican).
From 1984 to 1992, District 21 was a floterial district that contained Districts 14, 15, 16, 17, 18, 19, and 20. District 21 consisted of all of Ada County.
| Legislature | Session | Senate | House Seat A | House Seat B |
| 47th (1984 - 1986) | 1st | Jim Risch (R) | Boyd Hill (R) | Dean Sorensen (R) |
| 2nd | ||||
| 48th (1986 - 1988) | 1st | Sheila Sorensen (R) | ||
| 2nd | ||||
| 49th (1988 - 1990) | 1st | Mike Burkett (D) | ||
| 2nd | ||||
| 50th (1990 - 1992) | 1st | Al Lance (R) | ||
| 2nd |
From 1992 to 2002, District 21 consisted of Blaine, Camas, Lincoln Counties a portion of Elmore and Gooding Counties.
| Legislature | Session | Senate | House Seat A | House Seat B |
| 51st (1992 - 1994) | 1st | John Peavey (D) | Clint Stennett (D) | Pattie Nafziger (D) |
| 2nd | ||||
| 52nd (1994 - 1996) | 1st | Clint Stennett (D) | Wendy Jaquet (D) | Tim Ridinger (R) |
| 2nd | ||||
| 53rd (1996 - 1998) | 1st | |||
| 2nd | ||||
| 54th (1998 - 2000) | 1st | |||
| 2nd | ||||
| 55th (2000 - 2002) | 1st | |||
| 2nd |
From 2002 to 2012, District 21 consisted of a portion of Ada County.
| Legislature | Session | Senate | House Seat A | House Seat B |
| 57th (2002 - 2004) | 1st | Jack Noble (R) | Bill Sali (R) | Fred Tilman (R) |
| 2nd | Clifford Bayer (R) | |||
| 58th (2004 - 2006) | 1st | |||
| 2nd | Russ Fulcher (R) | |||
| 59th (2006 - 2008) | 1st | John Vander Woude (R) | ||
| 2nd | ||||
| 60th (2008 - 2010) | 1st | Rich Jarvis (R) | ||
| 2nd | ||||
| 61st (2010 - 2012) | 1st | John Vander Woude (R) | ||
| 2nd |
District 21 currently consists of a portion of Ada County.[1]
| Legislature | Session | Senate | House Seat A | House Seat B |
| 62nd (2012 - 2014) | 1st | Clifford Bayer (R) | Steven Harris (R) | Thomas Dayley (R) |
| 2nd | ||||
| 63rd (2014 - 2016) | 1st | |||
| 2nd | ||||
| 64th (2016 - 2018) | 1st | |||
| 2nd | ||||
| 65th (2018 - 2020) | 1st | Regina Bayer (R) | ||
| 2nd | Megan Kiska (R) | |||
| 66th (2020 - 2022) | 1st | Greg Ferch (R) | ||
| 2nd |