When was Easter first celebrated in colonial or antebellum America?I have checked every source I know, and have learned a lot about early...

Easter, of course, far predates the discovery of the New World.  It is the earliest Christian holiday, although exactly when it began to be celebrated as distinct from Pesach, or Passover, is unknown, although the early Church historian Eusebius tells us the dating of the celebration became a problem in the churches by the second century.  The name, at least according to 8th century historian the Venerable Bede derives from Eostre, Teutonic goddess of springtime, not surprising since early European Christians retained local festivals if they were at the same time of the year as Jewish festivals(logically enough).  In America Easter was celebrated from early on, but as a personal or familial holiday, not in large formal celebrations.  For one thing, the earliest colonists were Anglican and they did not hold formal religious holiday celebrations, a holdover from the Protestant Reformation (with religious wars still ongoing between Catholic and Protestant counties at the time).  The later Puritans of course held no religious holidays.  Of course there were Catholics in Virginia early on, and they celebrated Easter, as did some smaller Protestant groups especially among German or Norwegian immigrants.

Large scale formal celebration of Easter in the United States began following the War of Secession, or Civil War.  The religious revivals of the era just predating the war continued through the war and afterwards, and the sense that the nation had been crucified by the war and aftermath led to the Presbyterian Church holding large public ceremonies at Easter.  The scars of the war were equated with the scars of Christ, and the suffering of the people as a metaphor for those of Jesus.  From the Presbyterians the practice spread to other Protestant denominations.

The Easter Parade in New York has a documented history into the 1880s, but almost certainly began by the mid-1870s.  Large celebrations did take place in Boston and many cities around that time, but as to specifics on which church in which town presided over by which pastor, I'd be surprised if you could find out short of searching the individual church records of all still existing Presbyterian churches from that era.  As far as I know, which may not be far, there was no official Presbyterian declaration on the issue.  Obviously it began somewhere in the late 1860s or early '70s, but exactly where is probably lost to us.  Indications are it may have been in small-town Massachusetts.