Provided herein are compositions and methods for generating polypeptides using non-natural amino acids (nnAAs) and genetic machinery, wherein the modified polypeptides, such as therapeutic polypeptides, bind to albumin, such as serum albumin. Methods of substituting a non-natural amino acid in a first polypeptide to obtain a modified polypeptide, the nnAA in some instances comprising an albumin targeting group, are disclosed, as are methods for making populations of such modified polypeptides. A therapeutic polypeptide, interleukin-1 receptor antagonist (IL-1RA) is exemplified using the disclosed methods.