Here in Wood Dale, IL (near NW suburb of Chicago):
Daytime: WMVP
Nighttime: WMVP
DX/Retro: In the good old days, WCFL used to have a regular silent period every Monday morning, right after midnight. This of course produced some DX opportunities. This used to be the best bet to hear AM stations from Washington state as KOMO (Seattle) was heard several times with WCFL being off the air. My other 3 catches besides KOMO are KTOK (Oklahoma City, OK), XEOY (Mexico City) and HJAQ (Cartagena, Colombia). All of them during the WCFL silent periods.
Not exactly sure when the regular silent period stopped, but it must have been around the time WCFL became WLUP AM.
As mentioned above by tvnut, in 2006 WMVP operated under STA as a diplex from the WLS site in Tinley Park at a reduced power in order to replace the old towers with new ones. If I remember correctly this arrangement was only during daytime hours, so they could work on the replacement towers. During the night they would switch back to the Downer Grove site.
In recent developments, WMVP has applied to move their transmitter site to Joliet, IL and diplex with WCPT (820), since the land in Downers Grove was sold.