Yes, and some of them also fought on the side of Confederacy during the Civil War - estimated 1000-1500 vs 4000-6000 Poles on the Union side. For comparison Czechs were fighting mostly on the North side (**). Garibaldi's Italians , like the Poles, fought on both sides.
JSTOR: Polish American Studies, Vol. 22, No. 2 (Jul.-Dec., 1965), pp 99-106
POLES AND THE CONFEDERACY
Sigmund H. Uminski*
In 1861 at the outbreak of the Civil War, the Poles in the United States were estimated at 30,000. The Germans, the Irish, the French and others surpassed them in numbers. The call to arms by both the North and the South brought out hardened volunteers, the majority of whom had fought in wars of liberation on the Continent. The Polish American historian, Mieczyslaw Haiman, breaks down this effort to 4,000 for the North, and 1,000 for the South. Recent research reveals that this estimate may be revised upwards perhaps by fifty percent. This, of course, still gives a bare handful of Polish participants compared to the Germans, Irish and French.
This is followed by a description of the first official casualty of the War of Succession that was yet to begin. The 18 years old Thaddeus Strawinski was on duty in the Columbia Artillery at Fort Moultrie, when an accidental discharge of firearms seriously wounded him. He died on Ianuary 26, 1861, and the Charleston Mercury carried in its obituary of Ianuary 28, Strawinski's last words: "Friends, Oh! how sorry I am you are to attack Fort Sumter without me."
(*)Mn Uminski, a former PAHA vicepresident and currently an associate~editor of Polish-American Studies, read this essay at the Twenty-first Annual Meeting of the Association, Dec. 29, 1964, at Washington, D. C.
(**) Josef Skvorecki, a Czech-Canadian author, in his novel "The Bride of Texas" describes a little known fact of history: the formation of militia by a motley band of Czech immigrants who fought under General Sherman on his famous march to these. The novel has few interesting Polish threads as well.