I wanted to add a number of points (in my case there's 111 points in the data file, so it would be N = 111) under the legend.
sns.histplot(x, stat = 'density',
binwidth = 50,
kde = True,
color = 'red', alpha = .3,
kde_kws = {'cut': 2, 'bw_adjust': 0.5})
plt.legend(labels=["Sample_1"],
fontsize = 16)
plt.xlabel('Age', fontsize=18)
plt.ylabel('Density', fontsize=18)