We study equilibrium statistical mechanics of classical point counter-ions, formulated on 2D Euclidean space with logarithmic Coulomb interactions (infinite number of particles) or on the cylinder surface (finite particle numbers), in the vicinity of a single uniformly charged line (one single doublelayer), or between two such lines (interacting double-layers). The weak-coupling Poisson-Boltzmann theory, which applies when the coupling constant Γ is small, is briefly recapitulated (the coupling constant is defined as Γ ≡ βe 2 where β is the inverse temperature, and e the counter-ion charge). The opposite strong-coupling limit (Γ → ∞) is treated by using a recent method based on an exact expansion around the ground-state Wigner crystal of counter-ions. The weak-and strong-coupling theories are compared at intermediary values of the coupling constant Γ = 2γ (γ = 1, 2, 3), to exact results derived within a 1D lattice representation of 2D Coulomb systems in terms of anti-commuting field variables. The models (density profile, pressure) are solved exactly for any particles numbers N at Γ = 2 and up to relatively large finite N at Γ = 4 and 6. For the one-line geometry, the decay of the density profile at asymptotic distance from the line undergoes a fundamental change with respect to the mean-field behavior at Γ = 6. The like-charge attraction regime, possible in the strong coupling limit but precluded at mean-field level, survives for Γ = 4 and 6, but disappears at Γ = 2.