The arrangements for the grand base ball tournament to come off in (Decatur, Illinois) are progressing very favorably. The fair grounds have been secured and the exhibition ring will be leveled off for the grand trial of skill.The prospects are favorable for an immense gathering of ball players from all parts of the west, and the McPherson Club, under whose auspices the tournament is gotten up, are making every effort to insure success. The money necessary is not all subscribed, and we hope our citizens will not be backward in pledging the requisite amount. The time chosen, the middle of September, is one of the most delightful seasons of the year, and a better opportunity for an enjoyable time is not often afforded.
-The Decatur Republican, August 22, 1867
The Excelsior Base Ball Club of Chicago, which is probably the finest organization of the kind in the West, will positively be present at the tournament in this city next week. Is is expected that they will play the Union Base Ball Club, of St. Louis, on Thursday for the first grand prize, though the programme may be differently arranged to suit the exegencies of the occasion. The playing of these two crack clubs will doubtless attract an immense crowd of spectators.
-The Decatur Republican, September 12, 1867
The opening game of the Base Ball Tournament will be played to-morrow morning between the McPhersons, of Decatur, and the Excelsiors, of Pana, to be followed by the Bloomington Juniors vs. the Athletics, of Springfield.The Excelsiors, of Chicago, play the Bloomington Seniors on Thursday.
-Chicago Tribune, September 18, 1867
I can't find any evidence that the Union Club played in the Decatur tournament. The Chicago Tribune covered the event rather well and doesn't mention them. Interestingly, there seems to have been some controversy about which clubs were eligible to play in the tournament. Ten clubs were in Decatur on Wednesday and several others didn't show up until Wednesday night or Thursday morning (including the Excelsiors of Chicago). There had been a rule passed that a club had to be in Decatur by Wednesday evening to be eligible for the tournament but the rule was bent for the Excelsiors and this caused several clubs to withdraw in protest. It's possible that the Union Club didn't arrive in Decatur on time and was barred from the tournament or that they withdrew in protest over the favorable treatment received by the Excelsiors.
The Decatur tournament is, in and of itself, rather fascinating but I can't find any connection with the Union Club.