Is Tachanun recited by the Mincha prior to Erev Yom Kippur?
Tachanun is recited by Mincha of the 8th of Tishrei, which is the Mincha prior to Erev Yom Kippur.
 Admur 604:5; Siddur Admur; M”A 604:1; Levush 131:6; Kaf Hachaim 604:18; 584:74
 The reason: As the Yom Tov of Erev Yom Kippur is only accustomed to begin from nightfall even according to those opinions who view the night of Yom Kippur as a Yom Tov and thus decrease in Selichos and eat meat on the night of Erev Yom Kippur. [604:5]