WEEK-TV is the NBC-affiliated television station for North-Central Illinois that is licensed to Peoria. It broadcasts a high definition digital signal on UHF channel 25 from a transmitter at its studios on Springfield Road (along I-474) in East Peoria, a section of Groveland Township. Owned by Quincy Media, it operates and shares its facility with ABC/CW affiliate WHOI (owned by the Sinclair Broadcast Group) through joint sales and shared services agreements.
WEEK-TV signed-on February 1, 1953 transmitting an analog signal on UHF channel 43. It has always been an NBC affiliate. It was owned-and-operated by the Oklahoma City-based Oklahoma Publishing Company along with WEEK radio (1350 AM now WOAM) through its broadcasting subsidiary, West Central Broadcasting Company. Edward K. Gaylord was President, and the chairman of the board was United States Senator Robert S. Kerr (a former governor of Oklahoma and half of the Kerr-McGee Corporation). The original Chief Engineer of WEEK-AM-TV was Wayne Lovely, who supervised the construction of the stations' technical facilities and equipment installation in 1953 (he would remain employed by WEEK-TV until 1974).
On November 7, 1957, WEEQ-TV in La Salle launched as a full-time satellite of WEEK-TV in order to increase its signal reach.   The UHF channel 35 allocation was most recently used for TBN affiliate WWTO-TV which now broadcasts in digital on VHF channel 10 but retains 35 as its virtual channel via PSIP. WEEK-TV would move its analog signal to UHF channel 25 sometime around 1964. 
The channel 43 allocation was later moved from Peoria to Bloomington and used by the second incarnation of WBLN beginning in 1982 (this is now Fox affiliate WYZZ-TV).  In 1966, OPUBCO sold WEEK-TV and WEEQ-TV to Kansas City Southern Industries, which also acquired KRCG in Jefferson City, Missouri around the same time. The new owner eventually shut down WEEQ-TV sometime in the early-1970s.
In 1985, Kansas City Southern Industries sold both of its stations to Price Communications. On October 31, 1988, WEEK-TV and fellow NBC outlet KBJR-TV in Superior, Wisconsin became the two founding stations of the Granite Broadcasting Corporation. In 1997, WEEK-TV bought the broadcasting license for 98.5 in Eureka, gave it the call sign WEEK-FM, and nickname "Oldies 98.5". Granite Broadcasting divested itself of the radio station, which is now WPIA, in 1999. WEEK has been digital-only since February 17, 2009. 
On March 2, 2009, WEEK-TV took over the operations of rival WHOI (then owned by Barrington Broadcasting) through joint sales and shared services agreements. It resulted in that station closing its longtime studios on North Stewart Street in Creve Coeur and moving into WEEK-TV's East Peoria facility.  As a result of the consolidation, all five of Peoria's full-powered commercial television stations are now operated by two entities. Granite-owned CBS affiliate WTVH in Syracuse, New York (which were WHOI's original call letters) also saw its operations merged with Barrington-owned NBC affiliate WSTM-TV and low-powered CW affiliate WSTQ-LP on the very same day. In this case, however, WSTM is the senior partner in the operational arrangement with WTVH. 
On February 11, 2014, it was announced that Quincy-based Quincy Newspapers would acquire WEEK-TV, KBJR-TV, WBNG-TV in Binghamton, New York, and Malara Broadcasting-owned WPTA in Fort Wayne, Indiana from Granite Broadcasting. Originally, Quincy intended to continue providing services to WHOI but Sinclair (which had just completed its acquisition of Barrington Broadcasting back on November 25, 2013) gave notice that the JSA/SSA between WHOI and WEEK-TV (which was originally set to expire in March 2017) will be terminated within nine months of Quincy's consummation of WEEK-TV. On September 30, 2015, the FCC approved the purchase of WEEK by Quincy, and the sale was completed on November 2, nearly two years after the agreement was made.  
Until the end of 2014 through a separate joint sales agreement (JSA), WEEK-TV also controlled the market's MyNetworkTV outlet WAOE. That station, owned by Four Seasons Broadcasting, was based out of the Springfield Road studios during that operational arrangement. For awhile, the facility also hosted some internal operations (such as the maintenance of programming logs) of another Four Seasons-owned MyNetworkTV outlet, WBQD-LP (now WQAD-DT3). That station was actually controlled through a local marketing agreement with the Quad Cities' ABC affiliate, WQAD-TV (owned at the time by Local TV; now owned by Tribune Broadcasting) and maintained the majority of its day-to-day operations in the big three affiliate's studios in Moline.
On July 26, 2016, Quincy Media announced that it had acquired WHOI's ABC and CW affiliations, and would consolidate them onto subchannels of WEEK beginning August 1, 2016.
On June 5, 2006, WEEK-TV established a news share agreement with WAOE. The arrangement resulted in this station debuting a weeknight-only prime time newscast on the latter. Known as News 25 at Nine on My 59, the show could be seen for thirty minutes and offered competition to another weeknight half-hour production airing at the same time on WYZZ (produced by CBS affiliate WMBD-TV). WYZZ once aired a weekend edition of its newscast but this was dropped at some point in time. WAOE also provides a simulcast of WEEK-TV's weekday morning show (except for the first thirty-minute portion at 4:30 a.m.). After the JSA expired at the end of 2014, all WEEK-TV news programming was dropped from WAOE.
In March 2009 after becoming operated by WEEK-TV, WHOI shut down its separate news department and merged it with the NBC outlet. A new secondary set was built at the Springfield Road studios for use by WHOI in order to produce separate newscasts. That station let go most of its production and newscast personnel but added four on-air personalities to WEEK-TV's news team (three of them are still employed by WEEK-TV today). WHOI dropped its own weeknight newscasts at 5 and 6 for a new show seen at 5:30 so it would not directly compete with WEEK-TV's own programs in those time slots. WHOI continues to produce a separate weekday morning show (the two anchors for that program do not appear on WEEK-TV) and weeknight newscast at 10.
On weekends, WEEK-TV and WHOI simulcast local news but there can be a delay or pre-emption on one station because of network obligations (most notably sports programming). At some point in time after combining operations, the two outlets became the first news department in the market to upgrade local newscast production to 16:9 enhanced definition widescreen. Although not truly high definition, the shows match the aspect ratio of HD television screens. Longtime newsman Tom McIntyre retired from WEEK on May 21, 2015 after 42 years as nightly news anchor.