  We report measurements of the de Haas-van Alphen effect in the layered
heavy-fermion compound CePt$_2$In$_7$ in high magnetic fields up to 35 T. Above
an angle-dependent threshold field, we observed several de Haas-van Alphen
frequencies originating from almost ideally two-dimensional Fermi surfaces. The
frequencies are similar to those previously observed to develop only above a
much higher field of 45 T, where a clear anomaly was detected and proposed to
originate from a change in the electronic structure [M. M. Altarawneh et al.,
Phys. Rev. B 83, 081103 (2011)]. Our experimental results are compared with
band structure calculations performed for both CePt$_2$In$_7$ and
LaPt$_2$In$_7$, and the comparison suggests localized $f$ electrons in
CePt$_2$In$_7$. This conclusion is further supported by comparing
experimentally observed Fermi surfaces in CePt$_2$In$_7$ and PrPt$_2$In$_7$,
which are found to be almost identical. The measured effective masses in
CePt$_2$In$_7$ are only moderately enhanced above the bare electron mass $m_0$,
from 2$m_0$ to 6$m_0$.
