Well, you mentioned he possibly had a criminal background, so he could have been in prison on 1841 census night?
Or just away from home that night. I see a 55 yr old William Hill in Norton, with an elderly Joanna Hill.
Have you checked deaths 1841-1851?
yep i guess its possible he was in prison for the 41 census, or hospital?
theres further intrigue.... williams eldest son, samuel and his wife ann also were not recorded on the 1841 census. heres what i wrote in this families branch
"On the 1841 census, I cannot find Samuel or Ann anywhere, but Jemima (their daughter) is living with the Millingtons which seems strange, until we see Jemimas marriage in 1864 and her father is William Millington.
It appears that Ann had an affair, or was seduced (or raped?) by William Millington. Samuel and Ann had left the area to get her away from William? Hence no mention in 1841"
now i wonder whether samuels dad, william, took the law into his own hands here and did something to william millington. OR he could be living, somewhere, with his son samuel and ann .
william could also be buried with his first wife, ann, and daughter eliza (born 1807) - but i can find no trace of anns death, nor elizas.
ive not done a broad search for his deather 1841-51, but he is not at ockbrook or borrowash or recorded in the shardlow district (where he would have been).
see... its a complicated and patchy scene, but he must have been somewhere, either alive or dead.