We carried out UBVR _ { c } I _ { c } photometric study of three poorly studied young open clusters IC 1442 , King 21 , and Trumpler 7 ( Tr 7 ) . We obtained 263 , 244 , and 128 member stars using Gaia DR2 proper motions and parallaxes in IC 1442 , King 21 , and Tr 7 , respectively . The reddening , E ( B - V ) , was derived to be 0.54 \pm 0.04 , 0.76 \pm 0.06 , and 0.38 \pm 0.04 mag for these clusters . The comparison of observed colour-magnitude diagrams ( CMDs ) with solar metallicity isochrones yields log ( Age ) = 7.40 \pm 0.30 , 7.70 \pm 0.20 , and 7.85 \pm 0.25 yr and corresponding distances 2847 \pm 238 , 2622 \pm 156 , and 1561 \pm 74 pc for IC 1442 , King 21 , and Tr 7 , respectively . The estimated mass function ( MF ) slopes are found to be -1.94 \pm 0.18 , -1.54 \pm 0.32 , and -2.31 \pm 0.29 for IC 1442 , King 21 , and Tr 7 , respectively . The study of MF slopes determined separately in the inner and the outer regions of these clusters gives a steeper slope in outer region which suggests spatial variation in slope and mass segregation in the clusters . We found evidence of mass segregation after dynamical study in these clusters . The obtained relaxation time , T _ { E } , is 74 , 26 , and 34 Myr for the clusters IC 1442 , King 21 , and Tr 7 , respectively . The mass segregation in IC 1442 may be caused by early dynamical relaxation . The estimated T _ { E } is well below to the ages of King 21 and Tr 7 which indicates that these clusters are dynamically relaxed .