Paul is correct. Over 5,000 Germans volunteered at the St. Louis Arsenal in late April and May of 1861.
The total population of Missouri in 1860 was 1,182,012. Of those, 88,487 were German born and 43,464 were Irish born. St. Louis had roughly 60,000 Germans and 29,000 Irish. Although the Germans tended to be very antislavery, the Irish were often anti-abolitionist, because of the perceived competition from free blacks.