The station signed-on March 8, 1991 as KTMW and aired an analog signal on VHF channel 9. It was originally locally-owned by William Schuyler and affiliated with the Home Shopping Network (HSN). The call sign would change to KHDT-TV on April 13, 1992. Schuyler later sold the station to a subsidiary of Lambert Broadcasting, LLC. On January 16, 1995, it became a charter UPN affiliate, also carrying The WB programming on a secondary basis.
The call letters became KNIN-TV on August 30, 1996 and, during the first five years with those calls, the station was known as Boise's "no news" network and had a mascot news anchor named 'Rot Weiller'. The call letters are pronounced "canine", the Latin term for a dog. It phased out the news anchor mascot in 2002.
In late-1998, the station dropped WB programming, as the network decided to only air on cable outside the top 100 markets. Through national service The WB 100+, "KWOB" replaced KNIN as Boise's affiliate, and cleared the entire WB schedule. KNIN was eventually sold to Banks Broadcasting (50% of the company was owned by the LIN TV Corporation of Providence, Rhode Island).
On September 18, 2006, KNIN became an affiliate of The CW (the merger of UPN and The WB), carrying it on the main channel in place of UPN. A new second digital subchannel signed-on offering The CW Plus (a similar operation to The WB 100+) as the replacement for "KWOB". The former cable-exclusive station then dropped the faux calls in favor of KNIN-DT2. On July 1, 2008, Banks Broadcasting announced that it had agreed to sell KNIN to Journal Communications (owner of KIVI), creating Boise's first television duopoly.
The Federal Communications Commission (FCC) initially rejected the application on November 10; shortly afterward, Banks Broadcasting filed an appeal, and on January 16, 2009 the FCC reversed its decision, allowing the deal to go through. The purchase closed on April 24, at which point KNIN vacated its longtime studios on West Bannock Street in Downtown Boise and was integrated into KIVI's facilities in Nampa. On September 1, 2011, KNIN assumed the Fox affiliation from KTRV-TV, upon expiration of their CW affiliation agreements.
On September 12, CW Plus programming moved to KYUU-LP and a subchannel of KBOI-TV. The last CW program to air on KNIN was America's Next Top Model. KNIN's first Fox program was a repeat of Bones. Besides this television station sharing the same call sign with KNIN-FM 92.9 in Wichita Falls, Texas, there is no relation between the two. KNIN-DT2 previously carried the Live Well Network, it added Heroes & Icons on May 20, 2015.
On July 30, 2014, it was announced that The E.W. Scripps Company would acquire Journal Communications in an all-stock transaction. The combined firm will retain their broadcast properties and spin off their print assets as Journal Media Group. KNIN-TV, KIVI-TV and 5 radio stations, were not included in the merger; in September, Journal filed to transfer these stations to Journal/Scripps Divestiture Trust (with Kiel Media Group as trustee). The merge was completed on April 1, 2015 and Kiel Media Group assumed the operations of the license, Scripps retained KIVI. On May 7, 2015, Raycom Media agreed to purchase KNIN-TV for $14.5 million; Scripps will then enter into a shared services agreement that will allow KIVI to continue to provide services to KNIN. This arrangement is similar to one that the two companies have in West Palm Beach, Florida, where Raycom's Fox affiliate WFLX is operated through SSA by Scripps' NBC affiliate WPTV. The sale was completed on October 1, 2015.