Neat find. That party had an interesting history. It basically existed to promote immigration restrictions and anti-Catholic ideology. Fillmore never publicly spoke about his association with them. It folded into the Republican Party after 1856.
Yes, very interesting find. This was after Fillmore had already had his bad presidency but the Know Nothings drafted him to run again thinking he would add prestige and nostalgia to their party as the country was breaking up.