\startsetups chapter:after
    \ifcase\rawcountervalue[footnote]\relax
    \or
        \startsubject[title=Footnote]
            \placefootnotes
        \stopsubject
    \else
        \startsubject[title=Footnotes]
            \placefootnotes
        \stopsubject
    \fi
\stopsetups

\setupnotes[location=none]
\setupnotation[way=bychapter]

\setuphead[chapter][aftersection=\setups{chapter:after}]

\starttext
    \dorecurse{4}{
        \startchapter[title=Number #1]
            A few notes\dorecurse{\numexpr#1-1\relax}{\footnote{Note #1.##1}}.
        \stopchapter
    }
\stoptext
