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In the context of gauged U(1) extension of SM, we discuss the cosmological inflation scenarios, dark matter physics, and LHC phenomenology. We consider minimal U(1)$_X$ extended SM, a generalization of the minimal U(1)$_{B-L}$ model which is realized as a linear combination of the SM U(1)$_Y$ and the U(1)$_{B-L}$ gauge symmetries. In addition to a $B-L$ scalar and a new $Z^\prime$ gauge boson, the model also includes three generations of right handed neutrinos (RHNs) for the anomaly cancellation. With an identification of the $B-L$ scalar to be the inflaton field, we investigate inflection-point inflation which naturally accommodates inflation scenario with initial inflation scale below the Planck mass ($\phi_I \lesssim M_{Pl}$). For a renormalization group improved effective $\lambda \phi^4$ potential to develop an inflection-point with inflationary predictions consistent with the current cosmological observations, the mass ratios among the $Z^\prime$ guage boson, the RHNs, and the inflaton are fixed. In the $B-L$ limit with the gauge boson mass less than $1$ TeV we find that the scenario can be tested in the future collider experiments such as the High-Luminosity LHC and the SHiP experiments. On the other extreme, we consider the scenario such that the U(1)$_X$ gauge symmetry is mostly oriented towards the SM U(1)$_Y$ direction and investigate a consistency between the inflationary predictions and the latest LHC Run-2 results on narrow resonance $Z^\prime$ search with a di-lepton final state. Dark matter (DM) physics is another interesting possibility that we consider. Implementing $Z_2$ parity to one of the RHNs, we investigate the possibility of ``$Z^\prime$ -portal’’ DM scenario to explore the viable parameter region consistent with the relic abundance and the latest LHC Run-2 results on a narrow resonance $Z^\prime$ search with a di-lepton final state. Finally, we consider the prospect of RHN discovery at the LHC via $Z^\prime$ boson decay. U(1)$_X$ model provides significant enhancement of the production cross section of the RHNs from $Z^\prime$ decay in the future LHC experiments, which is crucial for the discovery of RHNs given that the production cross-section of $Z^\prime$ boson via di-lepton resonance is severely constrained. Taking this into account, we conclude that the possibility of discovering the RHNs in the future implies that the $Z^\prime$ boson will soon be discovered at the LHC.